Front matter (continued 5)

One of the most curious anomalies that may be met with in ornamental garden-plants is the conversion of stamens into pistils. It is neither common nor rare, but in most cases the change is so slight comparatively that it is ordinarily overlooked. In the opium-poppy, on the contrary, it is very showy, and heightens the ornamental effect of the young fruits after the fading of the flowers. Here the central capsule is surrounded by a large crown of metamorphosed stamens. This peculiarity has attracted the attention both of horticulturists and of botanists. As a rule not all the stamens are changed in this way but only those of the innermost rows. The outer stamens remain normal and fertile, and the flowers, when pollinated with their own pollen, bear as rich a harvest of seeds as other opium-poppies. The change affects both the filament and the anther, the former of which is dilated into a sheath. Within this sheath perfect [370] and more or less numerous ovules may be produced. The anthers become rudimentary and in their place broad leafy flaps are developed, which protrude laterally from the tip and constitute the stigmas. Ordinarily these altered organs are sterile, but in some instances a very small quantity of seed is produced, and when testing their viability I succeeded in raising a few plants from them. The same anomaly occurs in other plants. The common wall-flower (Cheiranthus Cheiri) and the houseleek (Sempervivum tectorum) are the best known instances. Both have repeatedly been described by various investigators. In compiling the literature of this subject it is very interesting to observe the two contrasting views respecting the nature of this anomaly. Some writers, and among them Masters in his "Vegetable Teratology" consider the deviations to be merely accidental. According to them some species are more subject to this anomaly than others, and the houseleek is said to be very prone to this change. Goeppert, Hofmeister and others occasionally found the pistilloid poppies in fields or gardens, and sowed their seeds in order to ascertain whether the accidental peculiarity was inheritable or not. On the other hand De Candolle in his "Prodromus" mentions the pistilloid wall-flowers as a distinct [371] variety, under the name of Cheiranthus Cheiri gynantherus, and the analogous form of the opium-poppy is not at all an accidental anomaly, but an old true horticultural variety, which can be bought everywhere under the names of Papaver somniferum monstruosum or polycephalum. Since it is an annual plant, only the seeds are for sale, and this at once gives a sufficient proof of its heredity. In all cases, where it was met with accidentally by botanists, it is to be assumed that stray seeds had been casually mixed with those of other varieties, or that the habit had been transmitted by a spontaneous cross. Wherever opportunity led to experiments on heredity, distinct races were found to be in possession of this quality, while others were not. It is of no use to cultivate large numbers of wall-flowers in the hope of one day seeing the anomaly arise; the only means is to secure the strain from those who have got it. With poppies the various varieties are so often intercrossed by bees, that the appearance of an accidental change may sometimes be produced, and in the houseleek the pistilloid warily seems to be the ordinary one, the normal strain being very rare or perhaps wholly wanting. Our three illustrative examples are good and permanent races, producing their peculiar qualities [372] regularly and abundantly. In this respect they are however very variable and dependent on external circumstances. Such a regularity is not met with in other instances. Often pedigree-experiments lead to poor races, betraying their tendency to deviate only from time to time and in rare cases. Such instances constitute what we have called in a former lecture, "half races," and their occurrence indicates that the casual observation of an anomaly is not in itself adequate to give an opinion as to the chance of repetition in sowing experiments. A large number of species seem to belong to this case, and their names may be found in the above mentioned work by Masters and elsewhere. But no effort has yet been made to separate thoroughly the pistilloid half-races from the corresponding ever-sporting varieties. Some plants are recorded as being more liable to this peculiarity than others. Stamens are sometimes replaced by open carpels with naked ovules arising from their edges and even from their whole inner surfaces. This may be seen in distinct strains of the cultivated bulbous Begonia, and more rarely in primroses. Here the apex of the carpellary leaf is sometimes drawn out into a long style, terminated by a flattened spatulate stigma. The pistillody of the stamens is frequently [373] combined with another deviation in the poppies. This is the growing together of some of the altered stamens so as to constitute smaller or larger connate groups. Often two are united, sometimes three, four or more. Flowers with numerous altered stamens are seldom wholly free from this most undesirable secondary anomaly. I call it undesirable with respect to experiments on the variability of the character. For it may easily be seen that while it is feasible to count the stamens even when converted into pistils, it is not possible when groups of them are more or less intimately united into single bodies. This combination makes all enumeration difficult and inaccurate and often wholly unreliable. In such cases the observation is limited to a computation of the degree of the change, rather than to a strict numerical inquiry. Happily the responses to the experimental influences are so marked and distinct that even this method of describing them has proved to be wholly sufficient. In extreme instances I have seen all the changed stamens of a flower of the opium-poppy united into a single body, so as to form a close sheath all around the central ovary. Lesser sheaths, surrounding one-half or one-third of the capsule are of course less rarely met with. Leaving this description of the outer appearance [374] of our anomaly, we may now consider it from the double point of view of inheritance and variability. The fact of inheritance is shown by the experience of many authors, and by the circumstance already quoted, that the variety has been propagated from seed for more than half a century, and may be obtained from various seed merchants. In respect to the variability, the variety belongs to the ever-sporting group, constituting a type which is more closely related to the "five-leaved" clover than to the striped flowers or even the double stocks. It fluctuates around an average type with half filled crowns, going as far as possible in both directions, but never transgressing either limit. It is even doubtful whether the presumable limits are, under ordinary circumstances, ever reached. Obviously one extreme would be the conversion of all the stamens, and the other the absolute deficiency of any marked tendency to such a change. Both may occur, and will probably be met with from time to time. But they must be extremely rare, since in my own extensive experiments, which were strictly controlled, I never was able to find a single instance of either of them. Some of the outer stamens have always remained unchanged, yielding enough pollen for the artificial pollination of [375] the central ovary, and on the other hand some rudiments of hardened filaments were always left, even if they were reduced to small protuberances on the thalamus of the flower. Between these extremes all grades occur. From single, partially or wholly changed stamens upwards to 150 and over, all steps may be seen. It is a true fluctuating variability. There is an average of between 50 and 100, constituting a nearly filled crown around the central capsule. Around this average the smaller deviations are most numerous and the larger ones more rare. The inspection of any bed of the variety suffices to show that, taken broadly, the ordinary laws of fluctuating variability are applicable. No counting of the single individuals is required to dispel all doubts on this point. Moreover all intermediate steps respecting the conversion of the single stamens may nearly always be seen. Rarely all are changed into normal secondary ovaries with a stigma and with a cavity filled with ovules. Often the stigma is incomplete or even almost wanting, in other instances the ovules are lacking or the cavity itself is only partially developed. Not rarely some stamens are reduced and converted into thin hard stalks, without any appearance of an ovary at their tip. But then the demarcation [376] between them and the thalamus fails, so that they cannot be thrown off when the flower fades away, but remain as small stumps around the base of the more fully converted filaments. This fact would frequently render the enumeration of the altered organs quite unreliable. For these reasons I have chosen a group of arbitrary stages in order to express the degree of deviation for a given lot of plants. The limits were chosen so as to be sufficiently trustworthy and easy to ascertain. In each group the members could be counted, and a series of figures was reached by this means which allowed of a further comparison of the competing sets of plants. It should be stated that in such experiments and especially in the case of such a showy criterion as the pistilloid heads afford after the time of flowering is over, the inspection of the controlling beds at once indicates the result of the experiment. Even a hasty survey is in most cases sufficient to get a definite conclusion. Where this is not the case, the counting of the individuals of the various groups often does not add to the evidence, and the result remains uncertain. On the other hand, the impression made by the groups of plants on the experimenter and on his casual visitors, cannot well be conveyed to the readers of his account by [377] other means than by figures. For this reason the result of the experiments is expressed in this way. I made six groups. The first includes the cases where the whole circle is reduced to small rudiments. The second shows 1-10 secondary capsules. The two following constitute half a crown around the central fruit, the third going up to this limit, the fourth going from this limit to a nearly filled circle. Wholly filled circles of secondary capsules without gaps give the two last degrees, the fifth requiring only continuity of the circle, the sixth displaying a large and bright crown all around the central head. The fifth group ordinarily includes from 90-100 altered stamens, while the sixth has from 100-150 of these deviating parts. In ordinary cultures the third and fourth group, with their interrupted crowns, predominate. Large crowns are rare and flowers which at first sight seem to be wholly normal, occur only under circumstances definitely known to be unfavorable to growth, and to the development of the anomaly. Having reached by this means a very simple and easy method of stating the facts shown by equal lots under contrasting influences, we will now make use of it to inquire into the relation [378] of this exceptionally high degree of variability to the inner and outer conditions of life. As a rule, all experiments show the existence of such a relation. Unfavorable conditions reduce the numbers of altered stamens, favorable circumstances raise it to its highest point. This holds true for lots including hundreds of specimens, but also for the sundry heads of one bed, and often for one single plant. We may compare the terminal flower with those of the lateral branches on a plant, and when no special influences disturb the experiment, the terminal head ordinarily bears the richest crown. If the first has more than 100 metamorphosed parts, the latter have often less than 50 on the same plant. In poor soil, terminal heads are often reduced to 10-20 monstrous organs, and in such cases I found the lateral flowers of the same plants ordinarily with less than 10 altered stamens. In some cases I allowed the branches of the third and fourth degree, in other words, the side twigs of the first branches of my selected plants to grow out and produce flowers in the fall. They were ordinarily weak, sometimes very small, having only 5-9 stigmas on their central fruit. Secondary capsules were not seen on such flowers, even when the experiment was repeated on a [379] somewhat larger scale and during a series of years. Among the same lot of plants individual differences almost always occur. They are partly due to inequalities already existing in the seeds, and partly to the diversity of the various parts of the same bed. Some of the plants become stout and have large terminal heads. Others remain very weak, with a slender stem, small leaves and undersized flowers. The height and thickness of the stem, the growth of the foliage and of the axillary buds are the most obvious measures of the individual strength of the plant. The development of the terminal flower and the size of its ovary manifestly depends largely on this individual strength, as may be seen at once by the inspection of any bed of opium-poppies. Now this size of the head can easily be measured, either by its height or circumference, or by its weight. Moreover we can arrange them into a series according to their size. If we do this with the polycephalous variety, the relation between individual strength and degree of metamorphosis at once becomes manifest. The largest heads have the brightest crowns, and the number of supernumerary carpels diminishes in nearly exact proportion to the size of the fruits. Fruits with less than 50 altered stamens weighed on an average 5 grams, [380] those with 50-100 such organs 7 grams and those with a bright crown 10 grams, the appendices being removed before the weighing. Corresponding results have been reached by the comparison of the height of the capsules with their abnormal surroundings. The degree of development of the monstrosity is shown by this observation to be directly dependent on, and in a sense proportionate to the individual strength of the plant. The differences between the specimens grown from a single lot of seeds, for instance from the seeds of one self-fertilized capsule are, as I have said, partly due to the divergences which are always present in a bed, even if the utmost care has been taken to make it as uniform as possible. These local differences are ordinarily underrated and overlooked, and it is often considered to be sufficient to cultivate small lots of plants under apparently similar conditions on neighboring beds, to be justified in imputing all the observed deviations of the plants to hereditary inequalities. This of course is true for large lots, whenever the averages only are compared. In smaller experiments the external conditions of the single individuals should always be considered carefully. Lots of one or two square meters suffice for such comparisons, but smaller lots are always subject to chances and [381] possibilities, which should never be left out of consideration. Therefore I will now point out some circumstances, which are ordinarily different on various parts of one and the same bed. In the first place comes the inequality of the seeds themselves. Some of them will germinate earlier and others later. Those that display their cotyledons on a sunny day will be able to begin at once with the production of organic food. Others appear in bad weather, and will thus be retarded in their development. These effects are of a cumulative nature as the young plants must profit by every hour of sunshine, according to the size of the cotyledons. Any inequality between two young seedlings is apt to be increased by this cumulative effect. The same holds good for the soil of the bed. It is simply impossible to mix the manure so equally that all individuals receive the same amount of it from the very beginning. I am in the habit of using manures in a dry and pulverized condition, of giving definite quantities to each square meter, and of taking the utmost care to get equal distribution and mixture with the soil, always being present myself during this most important operation. Nevertheless it is impossible to make the nourishment exactly equal for all the plants of even a small bed. [382] Any inequality from this cause will increase the difference in the size of the young leaves, augment the inequality of their production of organic matter and for this reason go on in an ever increasing rate. Rain and spraying, or on the other hand dryness of the soil, have still greater consequences. The slightest unevenness of the surface will cause some spots to dry rapidly and others to retain moisture during hours and even sometimes during days. Seeds, germinating in such little moist depressions grow regularly and rapidly, while those on the dryer elevations may be retarded for hours and days, before fully unfurling their seed-leaves. After heavy rains these differences may be observed to increase continually, and in some instances I found that plants were produced only on the wet spots, while the dry places remained perfectly bare. From this the wet spots seem to be the most favorable, but on the other hand, seeds may come to germinate there too numerously and so closely that the young plants will be crowded together and find neither space nor light enough, for a free and perfect development. The advantage may change to disadvantage in this way unless the superfluous individuals are weeded out in due time. [383] From all these and other reasons some plants will be favored by the external conditions from the beginning, while others will be retarded, and the effects will gradually increase until at last they become sufficient to account for a considerable amount of individual variability. There is no doubt that the difference in the strength of the plant and in the size of the capsules, going from 5-10 grams for a single fruit, are for the most part due to these unavoidable circumstances. I have tried all conceivable means to find remedies for these difficulties, but only by sowing my seeds in pans in a glass-house have I been able to reach more constant and equal conditions. But unfortunately such a method requires the planting out of the young seedlings in the beginning of the summer, and this operation is not without danger for opium-poppies, and especially not without important influence on the monstrosity of the pistilloid variety. Consequently my sowings of this plant have nearly always been made in the beds. In order to show how great the influence of all these little things may become, we only have to make two sowings on neighboring beds and under conditions which have carefully been made as equal as possible. If we use for these controlling experiments seeds from one and the same capsule, it will soon become evident that [384] no exact similarity between the two lots may be expected. Such differences as may be seen in these cases are therefore never to be considered of value when comparing two lots of seeds of different origin, or under varying conditions. No amount of accuracy in the estimation of the results of a trial, or in the counting out of the several degrees of the anomaly, is adequate to overcome the inaccuracy resulting from these differences. It is certainly of great importance to have a correct conception in regard to the influence of the surrounding conditions on the growth of a plant and on the development of the attribute we are to deal with. No less important is the question of the sensibility of the plants to these factors. Obviously this sensibility must not be expected to remain the same during the entire life-period, and periods of stronger and of weaker responses may be discerned. In the first place it is evident that external or inner influences are able to change the direction of the development of an organ only so long as this development is not yet fully finished. In the young flower-bud of the pistilloid poppy there must evidently be some moment in which it is definitely decided whether the young stamens will grow out normally or become metamorphosed into secondary pistils. From this [385] moment no further change of external conditions is able to produce a corresponding change in the degree of the anomaly. The individual strength of the whole plant may still be affected in a more or less manifest degree, but the number of converted stamens of the flower has been definitely fixed. The sensitive period has terminated. In order to determine the exact moment of this termination of the period of sensibility, I have followed the development of the flower buds during the first weeks of the life of the young plants. The terminal flower may already be seen in young plants only seven weeks old, with a stem not exceeding 5-6 cm. in height and a flower-bud with a diameter of nearly 1 mm., in which the stamens and secondary pistils are already discernible, but still in the condition of small rounded protuberances on the thalamus. Though it is not possible at that time to observe any difference between the future normal and converted stamens, it does not seem doubtful that the development is so far advanced, that in the inner tissues the decision has already definitely been taken. In the next few days this decision rapidly becomes visible, and the different parts of the normal stamens and the metamorphosed carpels soon become apparent. From this observation it [386] can be inferred that the sensitive period of the anomaly is limited for the terminal flower-head, to the first few weeks of the life of the young plants. The secondary heads manifestly leave this period at a somewhat later stage. In order to prove the accuracy of this conclusion I have tried to injure the anomalies after the expiration of the first six or seven weeks. I deprived them of their leaves, and damaged them in different ways. I succeeded in making them very weak and slender, without being able to diminish the number of the supernumerary carpels. The proportionality of the size of the central fruit and the development of the surrounding crown can often be modified or even destroyed by this means, and the apparent exceptions from this rule, which are often observed, may find their explanation in this way. In the second place I have tried to change the development of the anomaly during the period of sensibility, and even in the last part of it. This experiment succeeded fully when carried out within the fifth or sixth week after the beginning of the germination. As means of injury I transplanted the young plants. To this end I sowed my seeds in pans in unmanured soil, planted them out in little pots with richly prepared earth, grew them in these during a few weeks and afterwards transferred them to the [387] beds, taking care that the pats were removed, but the balls of earth not broken. In consequence of this treatment the plants became very large and strong, with luxuriant foliage and relatively numerous large flowers and fruits. But almost without exception they were poor in anomalous stamens, at least so on the terminal heads. On a lot of some 70 plants more than 50 had less than half a crown of secondary capsules, while from the same packet of seed the control-plants gave in an equal number more than half of filled crowns on all plants with the exception of five weak specimens. It is curious to compare such artificially injured plants with the ordinary cultures. Strong stems and heavy fruits, which otherwise are always indicative of showy crowns, now bear fruits wholly or nearly destitute of any anomalous change. The commonly prevailing rule seems to be reversed, showing thereby the possibility of abolishing the correlation between individual strength and anomaly by an artificial encroachment upon the normal conditions. Aside from these considerations the experiments clearly give proof of the existence of a period of sensibility limited to the first weeks of the life of the plant for the terminal flower. This knowledge enables us to explain many apparent [388] parent abnormalities, which may occur in the experiments. We now may take a broader view of the period of sensibility. Evidently the response to external influences will be greater the younger the organ. Sensibility will gradually diminish, and the phenomena observed in the last part of this period may be considered as the last remainder of a reaction which previously must have been much stronger and much readier, providing that it would be possible to isolate them from, and contrast them with, the other responses of the same plant. With the light thus cast upon the question, we may conclude that the sensitive period commences not only at the beginning of the germination, but must also be considered to include the life of the seed itself. From the moment of fertilization and the formation of the young embryo the development must be subjected to the influence of external agencies which determine the direction it will take and the degree of development it will finally be able to acquire. Probably the time of growth of the embryo and of the ripening of the seed correspond exactly to the period of highest sensibility. This period is only interrupted during the resting stage of the seed, to be repeated in germination. Afterwards the sensibility [389] slowly and gradually decreases, to end with the definite decision of all further growth sometime before the outer form of the organ becomes visible under the microscope. The last period of life includes only an expansion of the tissues, which may still have some influence on their final size, but not on their form. This has been definitely arrested before the end of the sensitive period, and ordinarily before the commencement of that rapid development, which is usually designated by the name of growth, as contrasted with evolution. Within the seed the evolution of the young plant manifestly depends upon the qualities and life-conditions of the parent-plant. The stronger this is, and the more favorable circumstances it is placed under, the more food will be available for the seed, and the healthier will be the development of the embryo. Only well-nourished plants give well-nourished seeds, and the qualities of each plant are for this reason at least, partly dependent on the properties of its parents and even of its grandparents. From these considerations the inference is forced upon us that the apparently hereditary differences, which are observed to exist among the seeds of a species or a variety and even of a single strain or a single parent-plant, may for a large part, and perhaps wholly, be the result [390] of the life-conditions of their parents and grandparents. Within the race all ssvariability would in this way be reduced to the effects of external circumstances. Among these nourishment is no doubt the most momentous, and this to such a degree that older writers designated the external conditions by the term nourishment. According to Knight nutrition reigns supreme in the whole realm of variability, the kind of food and the method of nourishment coming into consideration only in a secondary way. The amount of useful nutrition is the all-important factor. If this is so, and if nutrition decides the degree of deviation of any given character, the widest deviating individuals are the best nourished ones. The best nourished not only during the period of sensibility of the attribute under consideration, but also in the broadest sense of the word. This discussion casts a curious light upon the whole question of selection. Not of course upon the choice of elementary species or varieties out of the original motley assembly which nature and old cultures offer us, but upon the selection of the best individuals for isolation and for the improvement of the race. These are, according to my views, only the best nourished ones. Their external conditions have been the [391] most favorable, not only from the beginning of their own life in the field, but also during their embryonic stages, and even during the preparation of these latter in the life of their parents and perhaps even their grandparents. Selection then, would only be the choice of the best nourished individuals. In connection with the foregoing arguments I have tried to separate the choicest of the poppies with the largest crown of pistilloid stamens, from the most vigorous individuals. As we have already seen, these two attributes are as a rule proportional to one another. Exceptions occur, but they may be explained by some later changes in the external circumstances, as I have also pointed out. As a rule, these exceptions are large fruits with comparatively too few converted stamens; they are exactly the contrary from what is required for a selection. Or plants, which from the beginning were robust, may have become crowded together by further growth, and for these reasons become weaker than their congeners, though retaining the full development of the staminodal crown, which was fixed during the sensitive period and before the crowding. I have searched my beds yearly for several years in vain to find individuals which might recommend themselves for selection without having the stamp of permanent, [392] or at least temporarily better, nourishment. No starting-point for such an independent selection has ever been met with. Summing up the consequences of this somewhat extended discussion, we may state it as a rule that a general proportion between the individual strength and the degree of development of the anomaly exists. And from this point of view it is easy to see that all external causes which are known to affect the one, must be expected to influence the other also. It will therefore hardly be necessary to give a full description of all my experiments on the relations of the monstrosity to external conditions. A hasty survey will suffice. This survey is not only intended to convey an idea of the relations of pistilloid poppies to their environment, but may serve as an example of the principle involved. According to my experience with a large range of other anomalies, the same rule prevails everywhere. And this rule is so simple that exact knowledge of one instance may be considered as sufficient to enable us to calculate from analogy what is to be expected from a given treatment of any other anomaly. Our appreciation of observed facts and the conditions to be chosen for intended cultures are largely dependent on such calculations. What I am now going to describe [393] is to be considered therefore as an experimental basis for such expectations. First of all comes the question how many individuals are to be grown in a given place. When sowing plants for experimental purposes it is always best to sow in rows, and to give as few seeds to each row as possible, so as to insure all necessary space to the young plants. On the other hand the seeds do not all germinate, and after sowing too thinly, gaps may appear in the rows. This would cause not only a loss of space, but an inequality between the plants in later life, as those nearest the gaps would have more space and more light, and a larger area for their roots than those growing in the unbroken rows. Hence the necessity of using large quantities of seed and of weeding out a majority of young plants on the spots where the greatest numbers germinate. Crowded cultures as a rule, will give weak plants with thin stems, mostly unbranched and bearing only small capsules. According to the rule, these will produce imperfect crowns of secondary pistils. The result of any culture will thus be dependent to a high degree on the number of individuals per square meter. I have sown two similar and neighboring beds with the thoroughly mixed seeds of parent-plants of the same strain and culture, using as much [394] as 2.5 cu. cm. per square meter. On one of the beds I left all the germinating plants untouched and nearly 500 of them flowered, but among them 360 were almost without pistillody, and only 10 had full crowns. In the other bed I weeded away more than half of the young plants, leaving only some 150 individuals and got 32 with a full crown, nearly 100 with half crowns and only 25 apparently without monstrosity. These figures are very striking. From the same quantity of seed, in equal spaces, by similar exposure and treatment I got 10 fully developed instances in one and 32 in the other case. The weeding out of supernumerary individuals had not only increased the percentage of bright crowns, but also their absolute number per square meter. So the greatest number of anomalies upon a given space may be obtained by taking care that not too many plants are grown upon it: any increase of the number beyond a certain limit will diminish the probability of obtaining these structures. The most successful cultures may be made after the maximum number of individuals per unit of area has been determined. A control-experiment was made under the same conditions and with the same seed, but allowing much less for the same space. I sowed only 1 cu. cm. on my bed of 2 square meters, and thereby avoided [395] nearly all weeding out. I got 120 plants, and among them 30 with full crowns of converted stamens, practically the same number as after the weeding out in the first experiment. This shows that smaller quantities of seed give an equal chance for a greater number of large crowns, and should therefore always be preferred, as it saves both seed and labor. Weeding out is a somewhat dangerous operation in a comparative trial. Any one who has done it often, knows that there is a strong propensity to root out the weaker plants and to spare the stronger ones. Obviously this is the best way for ordinary purposes, but for comparisons evidently one should not discriminate. This rule is very difficult in practice, and for this reason one should never sow more than is absolutely required to meet all requirements. Our second point is the manuring of the soil. This is always of the highest importance, both for normal and for anomalous attributes. The conversion of the stamens into pistils is in a large measure dependent upon the conditions of the soil. I made a trial with some 800 flowering plants, using one sample of seed, but sowing one-third on richly manured soil, one-third on an unprepared bed of my garden, and one-third on nearly pure sand. In all other respects the three groups were treated in the same way. Of [396] the manured plants one-half gave full crowns, of the non-manured only one-fifth, and on the sandy soil a still smaller proportion. Other trials led to the same results. I have often made use of steamed and ground horn, which is a manure very rich in nitrogenous substances. One-eighth of a kilo per square meter is an ample amount. And its effect was to increase the number of full crowns to an exceptional degree. In the controlling trial and under ordinary circumstances this figure reached some 50%, but with ground horn it came up as high as 90%. We may state this result by the very striking assertion that the number of large crowns in a given culture may be nearly doubled by rich manure. All other external conditions act in a similar manner. The best treatment is required to attain the best result. A sunny exposure is one of the most essential requisites, and in some attempts to cultivate my poppies in the shade, I found the pistillody strongly reduced, not a single full crown being found in the whole lot. Often the weather may be hurtful, especially during the earlier stages of the plants. I protected my beds during several trials by covering them with glass for a few weeks, until the young plants reached the glass covering. I got a normal number of full crowns, some 55%, at a time [397] when the weather was so bad as to reduce the number in the control experiments to 10%. It would be quite superfluous to give more details or to describe additional experiments. Suffice to say, that the results all point in the same direction, and that pistillody of the poppies always clearly responds to the treatment, especially to external conditions during the first few weeks, that is, during the period of sensitiveness. The healthier and the stronger the plants the more fully they will develop their anomaly. In conclusion something is to be said about the choice of the seed. Obviously it is possible to compare seeds of different origin by sowing and treating them in the same way, giving attention to all the points above mentioned. In doing so the first question will be, whether there is a difference between the seeds of strong plants with a bright crown around the head and those of weaker individuals with lesser development of the anomaly. It is evident that such a difference must be expected, since the nutrition of the seed takes place during the period of the greatest sensitiveness. But the experiments will show whether this effect holds good against the influences which tend to change the direction of the development of the anomaly during the time of germination. [398] The result of my attempt has shown that the choice of the seeds has a manifest influence upon the ultimate development of the monstrosity, but that this influence is not strong enough to overwhelm all other factors. The choice of the fullest or smallest crowns may be repeated during succeeding generations, and each time compared with a culture under average conditions. By this means we come to true selection-experiments, and these result in a notable and rapid change of the whole strain. By selecting the brightest crowns I have come up in three years from 40 to 90 and ultimately to 120 converted stamens in the best flower of my culture, and in selecting the smallest crowns I was able in three years to exclude nearly all good crowns, and to make cultures in which heads with less than half-filled crowns constituted the majority. But such selected strains always remain very sensitive to treatment, and by changing the conditions the effect may be wholly lost in a single year, or even turned in the contrary direction. In other words, the anomaly is more dependent on external conditions during the germinating period than on the choice of the seeds, providing these belong to the pistilloid variety and have not deteriorated by some crossing with other sorts. At the beginning of this lecture I stated that [399] no selection is adequate to produce either a pure strain of brightly crowned flower-heads without atavism, or to conduce to an absolute and permanent loss of the anomaly. During a series of years I have tested my plants in both directions, but without the least effect. Limits are soon reached on both sides, and to transgress these seems quite impossible. Taking these limits as the marks of the variety, and considering all fluctuations between them as responses to external influences working during the life of the individual or governing the ripening of the seeds, we get a clear picture of a permanent ever-sporting type. The limits are absolutely permanent during the whole existence of this already old variety. They never change. But they include so wide a range of variability, that the extremes may be said to sport into one another, so much the more so as one of the extremes is to be considered morphologically as the type of the variation, while the other extreme can hardly be distinguished from the normal form of the species.

I have previously dealt with the question of the hereditary tendencies that cause monstrosities. These tendencies are not always identical for the same anomaly. Two different types may generally, be distinguished. One of them constitutes a poor variety, the other a rich one. But this latter is abundant and the first one is poor in instances of exactly the same conformation. Therefore the difference only lies in the frequency of the anomaly, and not in its visible features. In discovering an instance of any anomaly it is therefore impossible to tell whether it belongs to a poor or to a rich race. This important question can only be answered by direct sowing-experiments to determine the degree of heredity. Monstrosities are often considered as accidents, and rightfully so, at least as long as they are considered from a morphological point of view. Physiology of course excludes all accidentality. And in our present ease it shows [401] that some internal hereditary quality is present, though often latent, and that the observed anomalies are to be regarded as responses of this innate tendency to external conditions. Our two types differ in the frequency of these responses. Rare in the poor race, they are numerous in the rich variety. The external conditions being the same for both, the hereditary factor must be different. The tendency is weak in the one and strong in the other. In both cases, according to my experience, it may be weakened or strengthened by selection and by treatment. Often to a very remarkable degree, but not so far as to transgress the limits between the two races. Such transgression may apparently be met with from time to time, but then the next generation generally shows the fallacy of the conclusion, as it returns more or less directly to the type from which the strain had been derived. Monstrosities should always be studied by physiologists from this point of view. Poor and rich strains of the same anomaly seem at first sight to be so nearly allied that it might be thought to be very easy to change the one into the other. Nevertheless such changes are not on record, and although I have made several attempts in this line, I never succeeded in passing the limit. I am quite convinced that sometime [402] a method will be discovered of arbitrarily producing such conversions, and perhaps the easiest way to attain artificial mutations may lie concealed here. But as yet not the slightest indication of this possibility is to be found, save the fallacious conclusions drawn from too superficial observations. Unfortunately the poor strains are not very interesting. Their chance of producing beautiful instances of the anomaly for which they are cultivated is too small. Exceptions to this rule are only afforded by those curious and rare anomalies, which command general attention, and of which, therefore, instances are always welcome. In such cases they are searched for with perseverance, and the fact of their rarity impresses itself strongly on our mind. Twisted stems are selected as a first example. This monstrosity, called biastrepsis, consists of strongly marked torsions as are seen in many species with decussate leaves, though as a rule it is very rare. Two instances are the most generally known, those of the wild valerian (Valeriana officinalis) and those of cultivated and wild sorts of teasels (Dipsacus fullonum, D. sylvestris, and others). Both of these I have cultivated during upwards of fifteen years, but with contradictory results. The valerian is a perennial herb, multiplying itself yearly by [403] slender rootstocks or runners producing at their tips new rosettes of leaves and in the center of these the flowering stem. My original plant has since been propagated in this manner, and during several years I preserved large beds with hundreds of stems, in others I was compelled to keep my culture within more restricted limits. This plant has produced twisted stems of the curious shape, with a nearly straight flag of leaves on one side, described by De Candolle and other observers, nearly every year. But only one or two instances of abnormal stems occurred in each year, and no treatment has been found that proved adequate to increase this number in any appreciable manner. I have sown the seeds of this plant repeatedly, either from normal or from twisted stems, but without better results. It was highly desirable to be able to offer instances of this rare and interesting peculiarity to other universities and museums, but no improvement of the race could be reached and I have been constrained to give it up. My twisted valerian is a poor race, and hardly anything can be done with it. Perhaps, in other countries the corresponding rich race may be hidden somewhere, but I have never had the good fortune of finding it. This good fortune however, I did have with the wild teasel or Dipsacus sylvestris. [404] Stems of this and of allied species are often met with and have been described by several writers, but they were always considered as accidents and nobody had ever tried to cultivate them. In the summer of 1885 I saw among a lot of normal wild teasels, two nicely twisted stems in the botanical garden of Amsterdam. I at once proposed to ascertain whether they would yield a hereditary race and had all the normal individuals thrown away before the flowering time. My two plants flowered in this isolated condition and were richly pollinated by insects. Of course, at that time, I knew nothing of the dependency of monstrosities on external conditions, and made the mistake of sowing the seeds and cultivating the next generation in too great numbers on a small space. But nevertheless the anomaly was repeated, and the aberrant individuals were once more isolated before flowering. The third generation repeated the second, but produced sixty twisted stems on some 1,600 individuals. The result was very striking and quite sufficient for all further researches, but the normal condition of the race was not reached. This was the case only after I had discovered the bad effects of growing too many plants in a limited space. In the fourth generation I restricted my whole culture to about 100 individuals, and by this simple [405] means at once got up to 34% of twisted stems. This proportion has since remained practically the same. I have selected and isolated my plants during five succeeding generations, but without any further result, the percentage of twisted stems fluctuating between 30 and about 45 according to the size of the cultures and the favorableness or unfavorableness of the weather. It is very interesting to note that all depends on the question whether one has the good fortune of finding a rich race or not, as this pedigree-culture shows. Afterwards everything depends on treatment and very little on selection. As soon as the treatment becomes adequate, the full strength of the race at once displays itself, but afterwards no selection is able to improve it to any appreciable amount. Of course, in the long run, the responses will be the same as those of the pistilloid poppies on the average, and some influence of selection will show itself on closer scrutiny. Compared with the polycephalous poppies my race of twisted teasels is much richer in atavists. They are never absent, and always constitute a large part of each generation and each bed, comprising somewhat more than half of the individuals. Intermediate stages between them and the wholly twisted stems are not wanting, [406] and a whole series of steps may easily be observed from sufficiently large cultures. But they are always relatively rare, and any lot of plants conveys the idea of a dimorphous race, the small twisted stems contrasting strongly with the tall straight ones. A sharper contrast between good representatives of a race and their atavists is perhaps to be seen in no other instance. All the details contribute to the differentiation in appearance. The whole stature of the plants is affected by the varietal mark. The atavists are not, as in the case of the poppies, obviously allied with the type by a full range of intermediate steps, but quite distant from it by their rarity. There seems to be a gap in the same way as between the striped flowers of the snapdragon and their uniform red atavists, while with the poppies the atavists may be viewed as being only the extremes of a series of variations fluctuating around some average type. From this reason it is as interesting to appreciate the hereditary position of the atavists of twisted varieties as it was for the red-flowered descendants of the striped flowers. In order to ascertain this relation it is only necessary to isolate some of them during the blooming-period. I made this experiment in the summer of 1900 with the eighth generation of my race, and contrived [407] to isolate three groups of plants by the use of parchment bags, covering them alternately, so the flowers of only one group were accessible to insects, at a time. I made three groups, because the atavists show two different types. Some specimens have decussate stems, others bear all their leaves in whorls of three, but in respect to the hereditary tendency of the twisting character this difference does not seem to be of any importance. In this way I got three lots of seeds and sowed enough of them to have three groups of plants each containing about 150-200 well developed stems. Among these I counted the twisted individuals, and found nearly the same numbers for all three. The twisted parents gave as many as 41% twisted children, but the decussate atavists gave even somewhat more, viz., 44%, while the ternate specimens gave 37%. Obviously the divergences between these figures are too slight to be dwelt upon, but the fact that the atavists are as true or nearly as true inheritors of the twisted race as the best selected individuals is clearly proved by this experience. It is evident that here we have a double race, including two types, which may be combined in different degrees. These combinations determine a wide range of changes in the stature of the plants, and it seems hardly right to use the [408] same term for such changes as for common variations. It is more a contention of opposite characters than a true phenomenon of simple variability. Or perhaps we might say that it is the effect of the cooperation of a very variable mark, the twisting, with a scarcely varying attribute of the normal structure of the stem. Between the two types an endless diversity prevails, but outwardly there are limits which are never transgressed. The double race is as permanent, and in this sense as constant, as any ordinary simple variety, both in external form, and in its intimate hereditary qualities. I have succeeded in discovering some other rich races of twisted plants. One of them is the Sweet William (Dianthus barbatus), which yielded, after isolation, in the second generation, 25% of individuals with twisted stems, and as each individual produces often 10 and more stems, I had a harvest of more than half a thousand of instances of this curious, and ordinarily very rare anomaly. My other race is a twisted variety of Viscaria oculata, which is still in cultivation, as it has the very consistent quality of being an annual. It yielded last summer (1903) as high a percentage as 65 of twisted individuals, many of them repeating the monstrosity on several branches. After some occasional observations Gypsophila paniculata [409] seems to promise similar results. On the other hand I have sowed in vain the seeds of twisted specimens of the soapwort and the cleavewort (Saponaria officinalis and Galium Aparine). These and some others seem to belong to the same group as the valerian and to constitute only poor or so-called half-races. Next to the torsions come the fasciated stems. This is one of the most common of all malformations, and consists, in its ordinary form, of a flat ribbon-like expansion of the stems or branches. Below they are cylindrical, but they gradually lose this form and assume a flattened condition. Sometimes the rate of growth is unequal on different portions or on the opposite sides of the ribbon, and curvatures are produced and these often give to the fasciation a form that might be compared with a shepherd's crook. It is a common thing for fasciated branches and stems to divide at the summit into a number of subdivisions, and ordinarily this splitting occurs in the lower part, sometimes dividing the entire fasciated portion. In biennial species the rosette of the root-leaves of the first year may become changed by the monstrosity, the heart stretching in a transverse direction so as to become linear. In the next year this line becomes the base from which the stem grows. In such cases the fasciated stems [410] are broadened and flattened from the very beginning, and often retain the incipient breadth throughout their further development. Species of primroses (Primula japonica and others), of buttercups (Ranunculus bulbosus), the rough hawksbeard (Crepis biennis), the Aster Tripolium, and many others could be given as instances. Some of these are so rare as to be considered as poor races, and in cultural trials do not produce the anomaly except in a very few instances. Heads of rye are found in a cleft condition from time to time, single at their base and double at the top, but this anomaly is only exceptionally repeated from seed. Flattened stems of Rubia tinctorum are not unfrequently met with on the fields, but they seem to have as little hereditary tendency as the split rye (Secale Cereale). Many other instances could be given. Both in the native localities and in pedigree-cultures such ribboned stems are only seen from time to time, in successive years, in annual and biennial as well as in perennial species. The purple pedicularis (Pedicularis palustris) in the wild state, and the sunflower among cultivated plants, may be cited instead of giving a long list of analogous instances. On the other hand rich races of flattened stems are not entirely lacking. They easily betray [411] themselves by the frequency of the anomaly, and therefore may be found, and tried in the garden. Under adequate cultivation they are here as rich in aberrant individuals as the twisted races quoted above, producing in good years from 30-40% and often more instances. I have cultivated such rich races of the dandelion (Taraxacum officinale), of Thrincia hirta, of the dame's violet (Hesperis matronalis), of the hawkweed (Picris hieracioides), of the rough hawksbeard (Crepis biennis), and others. Respecting the hereditary tendencies these rich varieties with flattened stems may be put in the same category with the twisted races. Two points however, seem to be of especial interest and to deserve a separate treatment. The common cockscomb or Celosia cristata, one of the oldest and most widely cultivated fasciated varieties may be used to illustrate the first point. In beds it is often to be seen in quite uniform lots of large and beautiful crests, but this uniformity is only secured by careful culture and selection of the best individuals. In experimental trials such selection must be avoided, and in doing so a wide range of variability at once shows itself. Tall, branched stems with fan-shaped tops arise, constituting a series of steps towards complete atavism. This last [412] however, is not to be reached easily. It often requires several successive generations grown from seed collected from the most atavistic specimens. And even such selected strains are always reverting to the crested type. There is no transgression, no springing over into a purely atavistic form, such as may be supposed to have once been the ancestor of the present cockscomb. The variety includes crests and atavists, and may be perpetuated from both. Obviously every gardener would select the seeds of the brightest crests, but with care the full crests may be recovered, even from the worst reversionists in two or three generations. It is a double race of quite the same constitution as the twisted teasels. My second point is a direct proof of this assertion, but made with a fasciated variety of a wild species. I took for my experiment the rough hawksbeard. In the summer of 1895 I isolated some atavists of the fifth generation of my race, which, by ordinary selection, gave in the average from 20-40% of fasciated stems. My isolated atavists bore abundant fruit, and from these I had the next year a set of some 350 plants, out of which about 20% had broadened and linear rosettes. This proportion corresponds with the degree of inheritance which is shown in many years by the largest and strongest [413] fasciated stems. It strengthens our conclusion as to the innermost constitution of the double races or ever-sporting varieties. Twisted stems and fasciations are very striking monstrosities. But they are not very good for further investigation. They require too much space and too much care. The calculation of a single percentage requires the counting of some hundreds of individuals, taking many square meters for their cultivation, and this, as my best races are biennial, during two years. For this reason the countings must always be very limited, and selection is restrained to the most perfect specimens. Now the question arises, whether this mark is the best upon which to found selection. This seems to be quite doubtful. In the experiments on the heredity of the atavists, we have seen that they are, at least often, in no manner inferior to even the best inheritors of the race. This suggests the idea that it is not at all certain that the visible characters of a given individual are a trustworthy measure of its value as to the transmission of the same character to the offspring. In other words, we are confronted with the existence of two widely different groups of characters in estimating the hereditary tendency. One is the visible quality of the individuals and the other is the direct observation [414] of the degree in which the attribute is transmitted. These are by no means parallel, and seem in some sense to be nearly independent of each other. The fact that the worst atavists may have the highest percentage of varietal units seems to leave no room for another explanation. Developing this line of thought, we gradually arrive at the conclusion that the visible attribute of a varying individual is perhaps the most untrustworthy and the most unreliable character for selection, even if it seems in many cases practically to be the only available one. The direct determination of the degree of heredity itself is obviously preferable by far. This degree is expressed by the proportion of its inheritors among the offspring, and this figure therefore should be elevated to the highest rank, as a measure of the hereditary qualities. Henceforward we will designate it by the name of hereditary percentage. In scientific experiments this figure must be determined for every plant of a pedigree-culture singly, and the selection should be founded exclusively or at least mainly on it. It is easily seen that this method requires large numbers of individuals to be grown and counted. Some two or three hundred progeny of one plant are needed to give the decisive figure for this one [415] individual, and selection requires the comparison of at least fifty or more individuals. This brings the total amount of specimens to be counted up to some tens of thousands. In practice, where important interests depend upon the experiments, such numbers are usually employed and often exceeded, but for the culture of monstrosities, other methods are to be sought in order to avoid these difficulties. The idea suggests itself here that the younger the plants are, when showing their distinguishing marks, the more of them may be grown on a small space. Hence the best way is to choose such attributes, as may already be seen in the young seedlings, in the very first few weeks of their lives. Fortunately the seed-leaves themselves afford such distinctive marks, and by this means the plants may be counted in the pans, requiring no culture at all in the garden. Only the selected individuals need be grown to ripen their seeds, and the whole selection may be made in the spring, in the glasshouse. Instead of being very troublesome, the determination of the hereditary percentages becomes a definite reduction of the size of the experiments. Moreover it may easily be effected by any one who cares for experimental studies, but has not the means required for cultures on a larger scale. And lastly, there are [416] a number of questions about heredity, periodicity, dependency on nourishment and other life conditions, and even about hybridizing, which may be answered by this new method. Seed-leaves show many deviations from the ordinary shape, especially in dicotyledonous plants. A very common aberration is the multiplication of their number, and three seed-leaves in a whorl are not rarely met with. The whorl may even consist of four, and in rare cases of five or more cotyledons. Cleft cotyledons are also to be met with, and the fissure may extend varying distances from the tips. Often all these deviations may be seen among the seedlings of one lot, and then it is obvious that together they constitute a scale of cleavages, the ternate and quaternate whorls being only cases where the cleaving has reached its greatest development. All in all it is manifest that here we are met by one type of monstrosity, but that this type allows of a wide range of fluctuating variability. For brevity's sake all these cleft and ternate, double cleft and quaternate cotyledons and even the higher grades are combined under one common name and indicated as tricotyls. A second aberration of young seed-plants is exactly opposite to this. It consists of the union of the two seed-leaves into a single organ. This ordinarily betrays its origin by [417] having two separate apices, but not always. Such seedlings are called syncotyledonous or syncotyls. Other monstrosities have been observed from time to time, but need not be mentioned here. It is evident that the determination of the hereditary percentage is very easy in tricotylous or syncotylous cultures. The parent plants must be carefully isolated while blooming. Many species pollinate themselves in the absence of bees; from these the insects are to be excluded. Others have the stamens and stigmas widely separated and have to be pollinated artificially. Still others do not lend themselves to such operations, but have to be left free to the visits of bees and of humble-bees, this being the only means of securing seed from every plant. At the time of the harvest the seeds should be gathered separately from each plant, and this precaution should also be observed in studies of the hereditary percentage at large, and in all scientific pedigree-cultures. Every lot of seeds is to be sown in a separate pan, and care must be taken to sow such quantities the three to four hundred seedlings will arise from each. As soon as they display their cotyledons, they are counted, and the number is the criterion of the parent-plant. Only parent-plants with the highest percentages are selected, and out of [418] their seedlings some fifty or a hundred of the best ones are chosen to furnish the seeds for the next generation. This description of the method shows that the selection is a double one. The first feature is the hereditary percentage. But then not all the seedlings of the selected parents can be planted out, and a choice has to be made. This second selection may favor the finest tricotyls, or the strongest individuals, or rely on some other character, but is unavoidable. We now come to the description of the cultures. Starting points are the stray tricotyls which are occasionally found in ordinary sowings. In order to increase the chance of finding them, thousands of seeds of the same species must be inspected, and the range of species must be widened as much as possible. Material for beginning such experiments is easily obtained, and almost any large sample of seeds will be found suitable. Some tricotyls will be found among every thousand seedlings in many species, while in others ten or a hundred times, as many plants must be examined to secure them, but species with absolutely pure dicotylous seeds are very rare. The second phase of the experiment, however, is not so promising. Some species are rich, and others are poor in this anomaly. This difference [419] often indicates what can be expected from further culture. Stray tricotyls point to poor species or half-races, while more frequent deviations suggest rich or double-races. In both cases however, the trial must be made, and this requires the isolation of the aberrant individuals and the determination of their hereditary percentage. In some instances the degree of their inheritance is only a very small one. The isolated tricotyls yield 1 or 2% of inheritors, in some cases even less, or upwards up to 3 or 4%. If the experiment is repeated, no amelioration is observed, and this result remains the same during a series of successive generations. In the case of Polygonum convolvulus, the Black bindweed, I have tried as many as six generations without ever obtaining more than 3%. With other species I have limited myself to four successive years with the same negative result, as with spinage, the Moldavian dragon-head, (Dracocephalum moldavicum), and two species of corn catch-fly (Silene conica and S. conoidea). Such poor races hardly afford a desirable material for further inquiries. Happily the rich races, though rare, may be discovered also from time to time. They seem to be more common among cultivated plants and horticultural as well as agricultural species may be used. Hemp [420] and mercury (Mercurialis annua) among the first, snapdragon, poppies, Phacelia, Helichrysum, and Clarkia among garden-flowers may be given as instances of species containing the rich tricotylous double races. It is very interesting to note how strong the difference is between such cases and those which only yield poor races. The rich type at once betrays itself. No repeated selection is required. The stray tricotyls themselves, that are sought out from among the original samples, give hereditary percentages of a much higher type after isolation than those quoted above. They come up to 10-20% and in some cases even to 40%. As may be expected, individual differences occur, and it must even be supposed that some of the original tricotyls may not be pure, but hybrids between tricotylous and dicotylous parents. These are at once eliminated by selection, and if only the tricotyls which have the highest percentages are chosen for the continuance of the new race, the second generation comes up with equal numbers of dicotyls and tricotyls among the seedlings. The figures have been observed to range from 51-58% in the majority of the cases, and average 55%, rarely diverging somewhat more from this average. Here we have the true type of an ever-sporting variety. Every year it produces in the [421] same way heirs and atavists. Every plant, if fertilized with its own pollen, gives rise to both types. The parent itself may be tricotylous or dicotylous, or show any amount of multiplication and cleavage in its seed-leaves, but it always gives the entire range among its progeny of the variation. One may even select the atavists, pollinate them purely and repeat this in a succeeding generation without any chance of changing the result. On an average the atavists may give lower hereditary figures, but the difference will be only slight. Such tricotylous double races offer highly interesting material for inquiries into questions of heredity, as they have such a wide range of variability. There is little danger in asserting that they go upwards to nearly 100%, and downwards to 0%, diverging symmetrically on both sides of their average (50-55%). These limits they obviously cannot transgress, and are not even able to reach them. Samples of seed consisting only of tricotyls are very rare, and when they are met with the presumption is that they are too few to betray the rare aberrants they might otherwise contain. Experimental evidence can only be reached by the culture of a succeeding generation, and this always discloses the hidden qualities, showing that the double [422] type was only temporarily lost, but bound to return as soon as new trials are made. This wide range of variability between definite limits is coupled with a high degree of sensibility and adequateness to the most diverging experiments. Our tricotylous double races are perhaps more sensitive to selection than any other variety, and equally dependent on outer circumstances. Here, however, I will limit myself to a discussion of the former point. In the second generation after the isolation of stray tricotylous seedlings the average condition of the race is usually reached, but only by some of the strongest individuals, and if we continue the race, sowing or planting only from their offspring, the next generation will show the ordinary type of variability, going upwards in some and downwards in other instances. With the Phacelia and the mercury and some others I had the good luck in this one generation to reach as high as nearly 90% of tricotylous seedlings, a figure indicating that the normal dicotylous type had already become rare in the race. In other cases 80% or nearly 80% was easily attained. Any further divergence from the average would have required very much larger sowings, the effect of selection between a limited number of parents being only to retain the high degree once [423] reached; so for instance with the mercury, I had three succeeding generations of selection after reaching the average of 55%, but their extremes gave no increasing advance, remaining at 86, 92 and 91%. If we compare these results with the effects of selection in twisted and fasciated races, we observe a marked contrast. Here they reached their height at 30-40%, and no number of generations had the power of making any further improvement. The tricotyls come up in two generations to a proportion of about 54%, which shows itself to correspond to the average type. And as soon as this is reached, only one generation is required to obtain a very considerable improvement, going up to 80 or even 90%. It is evident that the cause of this difference does not lie in the nature of the monstrosity, but is due to the criterion upon which the selection is made. Selection of the apparently best individuals is one method, and it gives admirable results. Selection on the ground of the hereditary percentages is another method and gives results which are far more advantageous than the former. In the lecture on the pistillody of the poppies we limited ourselves to the selection of the finest individuals and showed that there is always a manifest correlation between the individual [424] strength of the plant and the degree of development of its anomaly. The same holds good with other monstrosities, and badly nourished specimens of rich races with twisted or fasciated stems always tend to reversion. This reversion, however, is not necessarily correlated with the hereditary percentage and therefore does not always indicate a lessening of the degree of inheritance. This shows that even in those cases an improvement may be expected, if only the means can be found to subject the twisted and the fasciated races to the same sharp test as the tricotylous varieties. Much remains to be done, and the principle of the selection of parents according to the average constitution of their progeny seems to be one of the most promising in the whole realm of variability. Besides tricotylous, the syncotylous seedlings may be used in the same way. They are more rarely met with, and in most instances seem to belong only to the unpromising half-races. The black bindweed (Polygonum Convolvulus), the jointed charlock (Raphanus Raphanistrum), the glaucous evening-primrose (Oenothera glauca) and many other plants seem to contain such half-races. On the other hand I found a plant of Centranthus macrosiphon yielding as much as 55% of syncotylous children [425] and thereby evidently betraying the nature of a rich or double race. Likewise the mercury was rich in such deviations. But the best of all was the Russian sunflower, and this was chosen for closer experiments. In the year of 1888 I had the good luck to isolate some syncotylous seedlings and of finding among them one with 19% of inheritors among its seeds. The following generation at once surpassed the ordinary average and came up in three individuals to 76, 81 and even 89%. My race was at once isolated and ameliorated by selection. I have tried to improve it further and selected the parents with the highest percentages during seven more generations; but without any remarkable result. I got figures of 90% and above, coming even in one instance up to the apparent purity of 100%. These, however, always remained extremes, the averages fluctuating yearly between 80-90% or thereabouts, and the other extremes going nearly every year downwards to 50%, the value which would be attained, if no selection were made. Contra-selection is as easily made as normal selection. According to our present principle it means the choice of the parents with the smallest hereditary percentage. One might easily imagine that by this means the dicotylous seedlings could be rendered pure. This, however, [426] is not at all the case. It is easy to return from so highly selected figures as for instance 95% to the average about of 50%, as regression to mediocrity is always an easy matter. But to transgress this average on the lower side seems to be as difficult as it is on the upper side. I continued the experiment during four succeeding generations, but was not able to go lower than about 10%, and could not even exclude the high figures from my strain. Parents with 65-75% of syncotylous seedlings returned in each generation, notwithstanding the most careful contra-selection. The attribute is inherent in the race, and is not to be eliminated by so simple a means as selection, nor even by a selection on the ground of hereditary percentages. We have dealt with torsions and fasciations and with seedling variations at some length, in order to point out the phases needing investigation according to recent views. It would be quite superfluous to consider other anomalies in a similar manner, as they all obey the same laws. A hasty survey may suffice to show what prospects they offer to the student of nature. First of all come the variegated leaves. They are perhaps the most variable of all variations. They are evidently dependent on external circumstances, and by adequate nutrition the leaves may even become absolutely white or [427] yellowish, with only scarcely perceptible traces of green along the veins. Some are very old cultivated varieties, as the wintercress, or Barbarea vulgaris. They continuously sport into green, or return from this normal color, both by seeds and by buds. Sports of this kind are very often seen on shrubs or low trees, and they may remain there and develop during a long series of years. Bud-sports of variegated holly, elms, chestnuts, beeches and others might be cited. One-sided variegation on leaves or twigs with the opposite side wholly green are by no means rare. It is very curious to note that variegation is perhaps the most universally known anomaly, while its hereditary tendencies are least known. Cristate and plumose ferns are another instance. Half races or rare accidental cleavages seem to be as common with ferns as cultivated double races, which are very rich in beautiful crests. But much depends on cultivation. It seems that the spores of crested leaves are more apt to reproduce the variety than those of normal leaves, or even of normal parts of the same leaves. But the experiments on which this assertion is made are old and should be repeated. Other cases of cleft leaves should also be tested. Ascidia are far more common than is usually believed. Rare instances point [428] to poor races, but the magnolias and lime-trees are often so productive of ascidia as to suggest the idea of ever-sporting varieties. I have seen many hundred ascidia on one lime-tree, and far above a hundred on the magnolia. They differ widely in size and shape, including in some cases two leaves instead of one, or are composed of only half a leaf or of even still a smaller part of the summit. Rich ascidia-bearing varieties seem to offer notable opportunities for scientific pedigree-cultures. Union of the neighboring fruits and flowers on flower-heads, of the rays of the umbellifers or of the successive flowers of the racemes of cabbages and allied genera, seem to be rare. The same holds good for the adhesion of foliar to axial organs, of branches to stems and other cases of union. Many of these cases return regularly in each generation, or may at least be seen from time to time in the same strains. Proliferation of the inflorescence is very common and changes in the position of staminate and pistillate flowers are not rare. We find starting points for new investigations in almost any teratological structure. Half-races and double-races are to be distinguished and isolated in all cases, and their hereditary qualities, the periodicity of the recurrence of the anomaly, the dependency on external circumstances [429] and many other questions have to be answered. Here is a wide field for garden experiments easily made, which might ultimately yield much valuable information on many questions of heredity of universal interest.

The chief object of all experimentation is to obtain explanations of natural phenomena. Experiments are a repetition of things occurring in nature with the conditions so guarded and so closely followed that it is possible to make a clear analysis of facts and their causes, it being rightfully assumed that the laws are the same in both cases. Experiments on heredity and the experience of the breeder find their analogy in the succession of generations in the wild state. The stability of elementary species and of retrograde varieties is quite the same under both conditions. Progression and retrogression are narrowly linked everywhere, and the same laws govern the abundance of forms in cultivated and in wild plants. Elementary species and retrograde varieties are easily recognizable. Ever-sporting varieties on the contrary are far less obvious, and in many cases their hereditary relations have [431] had to be studied anew. A clear analogy between them and corresponding types of wild plants has yet to be pointed out. There can be no doubt that such analogy exists; the conception that they should be limited to cultivated plants is not probable. Striped flowers and variegated leaves, changes of stamens into carpels or into petals may be extremely rare in the wild state, but the "five-leaved" clover and a large number of monstrosities cannot be said to be typical of the cultivated condition. These, however, are of rare occurrence, and do not play any important part in the economy of nature. In order to attain a better solution of the problem we must take a broader view of the facts. The wide range of variability of ever-sporting varieties is due to the presence of two antagonistic characters which cannot be evolved at the same time and in the same organ, because they exclude one another. Whenever one is active, the other must be latent. But latency is not absolute inactivity and may often only operate to encumber the evolution of the antagonistic character, and to produce large numbers of lesser grades of its development. The antagonism however, is not such in the exact meaning of the word; it is rather a mutual exclusion, because one of the opponents simply takes the place of the other when absent, or supplements [432] it to the extent that it may be only imperfectly developed. This completion ordinarily occurs in all possible degrees and thus causes the wide range of the variability. Nevertheless it may be wanting, and in the case of the double stocks only the two extremes are present. It is rather difficult to get a clear conception of the substitution, and it seems necessary to designate the peculiar relationship between the two characters forming such a pair by a simple name. They might be termed alternating, if only it were clearly understood that the alternation may be complete, or incomplete in all degrees. Complete alternation would result in the extremes, the incomplete condition in the intermediate states. In some cases as with the stocks, the first prevails, while in other cases, as with the poppies, the very extremes are only rarely met with. Taking such an alternation as a real character of the ever-sporting varieties, a wide range of analogous cases is at once revealed among the normal qualities of wild plants. Alternation is here almost universal. It is the capacity of young organs to develop in two diverging directions. The definitive choice must be made in extreme youth, or often at a relatively late period of development. Once made, this [433] choice is final, and a further change does not occur in the normal course of things. The most curious and most suggestive instance of such an alternation is the case of the water-persicaria or Polygonum amphibium. It is known to occur in two forms, one aquatic and the other terrestrial. These are recorded in systematic works as varieties, and are described under the names of P. amphibium var. natans Moench, and P. amphibium var. terrestre Leers or P. amphibium var. terrestris Moench. Such authorities as Koch in his German flora, and Grenier and Godron in their French flora agree in the conception of the two forms as varieties. Notwithstanding this, the two varieties may often be observed to sport into one another. They are only branches of the same plant, grown under different conditions. The aquatic form has floating or submerged stems with oblong or elliptic leaves, which are glabrous and have long petioles. The terrestrial plants are erect, nearly simple, more or less hispid throughout, with lanceolate leaves and short petioles, often nearly sessile. The aquatic form flowers regularly, producing its peduncle at right angles from the floating stems, but the terrestrial specimens are ordinarily seen without flower-spikes, which are but rarely met with, at least as far as my own experience goes. Intermediate [434] forms are very rare, perhaps wholly wanting, though in swamps the terrestrial plants may often vary widely in the direction of the floating type. That both types sport into each other has long been recognized in field-observations, and has been the ground for the specific name of amphibium, though in this respect herbarium material seems usually to be scant. The matter has recently been subjected to critical and experimental studies by the Belgian botanist Massart, who has shown that by transplanting the forms into the alternate conditions, the change may always be brought about artificially. If floating plants are established on the shore they make ascending hairy stems, and if the terrestrial shoots are submerged, their buds grow into long and slack, aquatic stems. Even in such experiments, intermediates are rare, both types agreeing completely with the corresponding models in the wild state. Among all the previously described cases of horticultural plants and monstrosities there is no clearer case of an ever-sporting variety than this one of the water-persicaria. The var. terrestris sports into the var. natans, and as often as the changing life conditions may require it. It is-true that ordinary sports occur without our discerning the cause and without [435] any relation to adaptation. This however is partly due to our lack of knowledge, and partly to the general rule that in nature only such sports as are useful are spared by natural selection, and what is useful we ordinarily term adaptive. Another side of the question remains to be considered. The word variety, as is now becoming generally recognized, has no special meaning whatever. But here it is assumed in the clearly defined sense of a systematic variety, which includes all subdivisions of species. Such subdivisions may be, from a biological point of view, elementary species and also be eversporting varieties. They may be retrograde varieties, and the two alternating types may be described as separate varieties. It is readily granted that many writers would not willingly accept this conclusion. But it is simply impossible to avoid it. The two forms of the water-persicaria must remain varieties, though they are only types of the different branches of a single plant. If not, hundreds and perhaps thousands of analogous cases are at once exposed to doubt, and the whole conception of systematic varieties would have to be thrown over. Biologists of course would have no objection to this, but the student of the flora of any given country [436] or region requires the systematic subdivisions and should always use his utmost efforts to keep them as they are. There is no intrinsic difficulty in the statement that different parts of the same plant should constitute different varieties. In some cases different branches of the same plant have been described as species. So for instance with the climbing forms of figs. Under the name of Ficus repens a fine little plant is quite commonly cultivated as a climber in flower baskets. It is never seen bearing figs. On the other hand a shrub of our hothouses called Ficus stipulata, is cultivated in pots and makes a small tree which produces quite large, though non-edible figs. Now these two species are simply branches of the same plant. If the repens is allowed to climb up high along the walls of the hothouses, it will at last produce stipulate branches with the corresponding fruits. Ficus radicans is another climbing form, corresponding to the shrub Ficus ulmifolia of our glasshouses. And quite the same thing occurs with ivy, the climbing stems of which never flower, but always first produce erect and free branches with rhombic leaves. These branches have often been used as cuttings and yield little erect and richly flowering shrubs, which are known in [437] horticulture under the varietal name of Hedera Helix arborea. Manifestly this classification is as nearly right as that of the two varieties of the water-persicaria. Going one step further, we meet with the very interesting case of alpine plants. The vegetation of the higher regions of mountains is commonly called alpine, and the plants show a large number of common features, differentiating them from the flora of lower stations. The mountain plants have small and dense foliage, with large and brightly-colored flowers. The corresponding forms of the lowlands have longer and weaker stems, bearing their leaves at greater distances, the leaves themselves being more numerous. The alpine forms, if perennial, have thick, strongly developed and densely branched rootstocks with heavy roots, in which a large amount of food material is stored up during the short summer, and is available during the long winter months of the year. Some species are peculiar to such high altitudes, while many forms from the lowlands have no corresponding type on the mountains. But a large number of species are common to both regions, and here the difference of course is most striking. Lotus corniculatus and Calamintha Acinos, Calluna vulgaris and Campanula [438] rotundifolia may be quoted as instances, and every botanist who has visited alpine regions may add other examples. Even the edelweiss of the Swiss Alps, Gnaphalium Leontopodium, loses its alpine characters, if cultivated in lowland gardens. Between such lowland and alpine forms intermediates regularly occur. They may be met with whenever the range of the species extends from the plains upward to the limit of eternal snow. In this case the systematists formerly enumerated the alpine plants as forma alpestris, but whenever the intermediate is lacking the term Varietas alpestris was often made use of. It is simply impossible to decide concerning the real relation between the alpine and lowland types without experiments. About the middle of the last century it was quite a common thing to collect plants not only for herbarium-material, but also for the purpose of planting them in gardens and thus to observe their behavior under new conditions. This was done with the acknowledged purpose of investigating the systematic significance of observed divergencies. Whenever these held good in the garden they were considered to be reliable, but if they disappeared they were regarded as the results of climatic conditions, or of the influence of soil or nourishment. Between [439] these two alternatives, many writers have tried to decide, by transplanting their specimens after some time in the garden, into arid or sandy soil, in order to see whether they would resume their alpine character. Among the systematists who tested plants in this way, Nageli especially, directed his attention to the hawkweeds or Hieracium. On the Swiss Alps they are very small and exhibit all the characters of the pure alpine type. Thousands of single plants were cultivated by him in the botanical garden of Munich, partly from seed and partly from introduced rootstocks. Here they at once assumed the tall stature of lowland forms. The identical individual, which formerly bore small rosettes of basal leaves, with short and unbranched flower-stalks, became richly leaved and often produced quite a profusion of flower-heads on branched stems. If then they were transplanted to arid sand, though remaining in the same garden and also under the same climatic conditions they resumed their alpine characters. This proved nutrition to be the cause of the change and not the climate. The latest and most exact researches on this subject are due to Bonnier, who has gone into all the details of the morphologic as well as of the physiologic side of the problem. [440] His purpose was the study of partial variability under the influence of climate and soil. In every experiment he started from a single individual, divided it into two parts and planted one half on a mountain and the other half on the plain. The garden cultures were made chiefly at Paris and Fontainebleau, the alpine cultures partly in the Alps, partly in the Pyrenees. From time to time the halved plants were compared with each other, and the cultures lasted, as a rule, during the lifetime of the individual, often covering many years. The common European frostweed or Helianthemum vulgare will serve to illustrate his results. A large plant growing in the Pyrenees in an altitude of 2,400 meters was divided. One half was replanted on the same spot, and the other near Cadeac, at the base of the mountain range (740 M.). In order to exclude the effect of a change of soil, a quantity of the earth from the original locality was brought into the garden and the plant put therein. Further control experiments were made at Paris. As soon as the two halved individuals commenced to grow and produced new shoots, the influence of the different climates made itself felt. On the mountain, the underground portions remained strong and dense, the leaves and internodes small and hairy, the flowering stems nearly [441] procumbent, the flowers being large and of a deep yellow. At Cadeac and at Paris the whole plant changed at once, the shoots becoming elongated and loose, with broad and flattened, rather smooth leaves and numerous pale-hued flowers. The anatomical structure exhibited corresponding differences, the intercellular spaces being small in the alpine plant and large in the one grown in the lowlands, the wood-tissues strong in the first and weak in the second case. The milfoil (Achillea Millefolium) served as a second example, and the experiments were carried on in the same localities. The long and thick rootstocks of the alpine plant bearing short stems only with a few dense corymbs contrasted markedly with the slender stems, loose foliage and rich groups of flowerheads of the lowland plant. The same differences, in inner and outer structures were observed in numerous instances, showing that the alpine type in these cases is dependent on the climate, and that the capacity for assuming the antagonistic characters is present in every individual of the species. The external conditions decide which of them becomes active and which remains inactive, and the case seems to be exactly parallel to that of the water-persicaria. In the experiments of Bonnier the influence of the soil was, as a rule, excluded by transplanting [442] part of the original earth with the transplanted half of the plant. From this he concluded that the observed changes were due to the inequality of the climate. This involved three main factors, light, moisture and temperature. On the mountains the light is more intense, the air drier and cooler. Control-experiments were made on the mountains, depriving the plants of part of the light. In various ways they were more or less shaded, and as a rule responded to this treatment in the same way as to transplantation to the plain below. Bonnier concluded that, though more than one factor takes part in inciting the morphologic changes, light is to be considered as the chief agency. The response is to be considered as a useful one, as the whole structure of the alpine varieties is fitted to produce a large amount of organic material in a short time, which enables the plants to thrive during the short summers and long winters of their elevated stations. In connection with these studies on the influences of alpine climates, Bonnier has investigated the internal structure of arctic plants, and made a series of experiments on growth in continuous electric light. The arctic climate is cold, but wet, and the structure of the leaves is correspondingly loose, though the plants become [443] as small as on the Alps. Continuous electric light had very curious effects; the plants became etiolated, as if growing in darkness, with the exception that they assumed a deep green tinge. They showed more analogy with the arctic than with the alpine type. The influence of the soil often produces changes similar to that of climate. This was shown by the above cited experiments of Nageli with the hawkweeds, and may easily be controlled in other cases. The ground-honeysuckle or Lotus corniculatus grows in Holland partly on the dry and sandy soil of the dunes, and occasionally in meadows. It is small and dense in the first case, with orange and often very darkly colored petals, while it is loose and green in the meadows, with yellower flowers. Numerous analogous cases might be given. On mountain slopes in South Africa, and especially in Natal, a species of composite is found, which has been introduced into culture and is used as a hanging plant. It is called Othonna crassifolia and has fleshy, nearly cylindrical leaves, and exactly mimics some of the crassulaceous species. On dry soil the leaves become shorter and thicker and assume a reddish tinge, the stems remain short and woody and bear their leaves in dense rosettes. On moist and rich garden-soil this aspect becomes [444] changed at once, the stems grow longer and of a deeper green. Intermediates occur, but notwithstanding this the two extremes constitute clearly antagonistic types. The flora of the deserts is known to exhibit a similar divergent type. Or rather two types, one adapted to paucity of water, and the other to a storage of fluid at one season in order to make use of it at other times, as is the case with the cactuses. Limiting ourselves to the alternate group, we observe a rich and dense branching, small and compact leaves and extraordinarily long roots. Here the analogy with the alpine varieties is manifest, and the dryness of the soil evidently affects the plants in a similar way, as do the conditions of life in alpine regions. The question at once comes up as to whether here too we have only instances of partial variability, and whether many of the typical desert-species would lose their peculiar character by cultivation under ordinary conditions. The varieties of Monardella macrantha, described by Hall, from the San Jacinto Mountain, Cal., are suggestive of such an intimate analogy with the cases studied by Bonnier, that it seems probable that they might yield similar results, if tested by the same method. Leaving now the description of these special [445] cases, we may resume our theoretical discussion of the subject, and try to get a clearer insight into the analogy of ever-sporting varieties and the wild species quoted. All of them may be characterized by the general term of dimorphism. Two types are always present, though not in the same individual or in the same organ. They exclude one another, and during their juvenile stage a decision is taken in one direction or in the other. Now, according to the theory of natural selection, wild species can only retain useful or at least innocuous qualities, since all mutations in a wrong direction must perish sooner or later. Cultivated species on the other hand are known to be largely endowed with qualities, which would be detrimental in the wild condition. Monstrosities are equally injurious and could not hold their own if left to themselves. These same principles may be applied to ever-sporting or antagonistic pairs of characters. According to the theory of mutations such pairs may be either useful or useless. But only the useful will stand further test, and if they find suitable conditions will become specific or varietal characters. On this conclusion it becomes at once clear, why natural dimorphism is, as a rule, a very useful quality, while the cultivated dimorphous varieties [446] strike us as something unnatural. The relation between cause and effect, is in truth other than it might seem to be at first view, but nevertheless it exists, and is of the highest importance. From this same conclusion we may further deduce some explanation of the hereditary races characterized by monstrosities. It is quite evident that the twisted teasels are inadequate for the struggle with their tall congeners, or with the surrounding plants. Hence the conclusion that a pure and exclusively twisted race would soon die out. The fact that such races are not in existence finds its explanation in this circumstance, and therefore it does not prove the impossibility or even the improbability that some time a pure twisted race might arise. If chance should put such an accidental race in the hands of an experimenter, it could be protected and preserved, and having no straight atavistic branches, but being twisted in all its organs, might yield the most curious conceivable monstrosity, surpassing even the celebrated dwarf twisted shrubs of Japanese horticulturists. Such varieties however, do not exist at present. The ordinary twisted races on the other hand, are found in the wild state and have only to be isolated and cultivated to yield large numbers [447] of twisted individuals. In nature they are able to maintain themselves during long centuries, quite as well as normal species and varieties. But they owe this quality entirely to their dimorphous character. A twisted race of teasels might consist of successive generations of tall atavistic individuals, and produce yearly some twisted specimens, which might be destroyed every time before ripening their seeds. Reasoning from the evidence available, and from analogous cases, the variety would, even under such extreme circumstances, be able to last as long as any other good variety or elementary species. And it seems to me that this explanation makes clear how it is possible that varieties, which are potentially rich in their peculiar monstrosity, are discovered from time to time among plants when tested by experimental methods. Granting these conclusions, monstrosities on the one side, and dimorphous wild species on the other, constitute the most striking examples of the inheritance of latent characters. The bearing of the phenomena of dimorphism upon the principles of evolution formulated by Lamarck, and modified by his followers to constitute Neo-Lamarckianism, remains to be considered. Lamarck assumed that the external conditions directly affected the organisms in [448] such a way as to make them better adapted to life, under prevailing circumstances. Nageli gave to this conception the name "Theory of direct causation" (Theorie der directen Bewirkung), and it has received the approval of Von Wettstein, Strasburger and other German investigators. According to this conception a plant, when migrating from lowlands into the mountains would slowly be changed and gradually assume alpine habits. Once acquired this habit would become fixed and attain the rank of specific characters. In testing this theory by field-observations and culture-experiments, the defenders of the Nagelian principle could easily produce evidence upon the first point. The change of lowland-plants into alpine varieties can be brought about in numerous cases, and corresponding changes under the influence of soil, or climate, or life-conditions are on record for the most various characters and qualities. The second point, however, is as difficult to prove as the first is of easy treatment. If after hundreds and thousands of years of exposure to alpine or other extreme conditions a fixed change is proved to have taken place, the question remains unanswered, whether the change has been a gradual or a sudden one. Darwin pointed out that long periods of life afford a [449] chance for a sudden change in the desired direction, as well as for the slow accumulation of slight deviations. Any mutations in a wrong direction would at once be destroyed, but an accidental change in a useful way would be preserved, and multiply itself. If in the course of centuries this occurred, they would be nearly sure to become established, however rare at the outset. Hence the positive assertion is scarcely capable of direct proof. On the other hand the negative assertion must be granted full significance. If the alpine climate has done no more than produce a transitory change, it is clear that thousands of years do not, necessarily, cause constant and specific alterations. This requirement is one of the indispensable supports of the Lamarckian theory. The matter is capable of disproof however, and such disproof seems to be afforded by the direct evidence of the present condition of the alpine varieties at large, and by many other similar cases. Among these the observations of Holtermann on some desert-plants of Ceylon are of the highest value. Moreover they touch questions which are of wide importance for the study of the biology of American deserts. For this reason I may be allowed to introduce them here at some length. [450] The desert of Kaits, in Northern Ceylon, nourishes on its dry and torrid sands some species, represented by a large number of individuals, together with some rarer plants. The commonest forms are Erigeron Asteroides, Vernonia cinerea, Laurea pinnatifida, Vicoa auriculata, Heylandia latebrosa and Chrysopogon montanus. In direct contrast with the ordinary desert-types they have a thin epidermis, with exposed stomata, features that ordinarily were characteristic of species of moister regions. They are annuals, growing rapidly, blooming and ripening their seeds before the height of the dry season. Evidently they are to be considered as the remainder of the flora of a previous period, when the soil had not yet become arid. They might be called relics. Of course they are small and dwarf-like, when compared with allied forms. These curious little desert-plants disprove the Nagelian views in two important points. First, they show that extreme conditions do not necessarily change the organisms subjected to them, in a desirable direction. During the many centuries that these plants must have existed in the desert in annual generations, no single feature in the anatomical structure has become changed. Hence the conclusion that small leaves, abundant rootstocks and short [451] stems, a dense foliage, a strongly cuticularized epidermis, few and narrow air-cavities in the tissues and all the long range of characteristics of typical desert-plants are not a simple result of the influence of climate and soil. There is no direct influence in this sense. The second point, in which Nageli's idea is broken down by Holtermann's observations, results from the behavior of the plants of the Kaits desert when grown or sown on garden soil. When treated in this way they at once lose the only peculiarity which might be considered as a consequence of the desert-life of their ancestors, their dwarf stature. They behave exactly like the alpine plants in Bonnier's experiments, and with even more striking differences. In the desert they attain a height of a few centimeters, but in the garden they attain half a meter and more in height. Nothing in the way of stability has resulted from the action of the dry soil, not even in such a minor point as the height of the stems. From the facts and discussions we may conclude that double adaptation is not induced by external influences, at least not in any way in which it might be of use to the plant. It may arise by some unknown cause, or may not be incited at all. In the first case the plant becomes capable of living under the alternating [452] circumstances, and if growing near the limits of such regions it will overlap and get into the new area. All other species, which did not acquire the double habit, are of course excluded, with such curious exceptions as those of Kaits. The typical vegetation under such extreme conditions however, finds explanation quite as well by the one as by the other view. Leaving these obvious cases of double adaptation, there still remains one point to be considered. It is the dwarf stature of so many desert and alpine plants. Are these dwarfs only the extremes of the normal fluctuating variability, or is their stature to be regarded as the expression of some peculiar adaptive but latent quality? It is as yet difficult to decide this question, because statistical studies of this form of variability are still wanting. The capacity of ripening the seed on individuals of dwarf stature however, is not at all a universal accompaniment of a variable height. Hence it cannot be considered as a necessary consequence of it. On the other hand the dwarf varieties of numerous garden-plants, as for instance: of larkspurs, snapdragon, opium-poppies and others are quite stable and thence are obviously due to peculiar characteristics. Such characteristics, if combined with tall stature into a pair of antagonists, would yield a double [453] adaptation, and on such a base a hypothetical explanation could no doubt be rested. Instead of discussing this problem from the theoretical side, I prefer to compare those species which are capable of assuming a dwarf stature under less uncommon conditions than those of alpine and desert-plants. Many weeds of our gardens and many wild species have this capacity. They become very tall, with large leaves, richly branched stems and numerous flowers in moist and rich soil. On bad soil, or if germinating too late, when the season is drier, they remain very small, producing only a few leaves and often limiting themselves to one flower-head. This is often seen with thorn-apples and amaranths, and even with oats and rye, and is notoriously the case with buckwheat. Gauchery has observed that the extremes differ often as much from one another as 1:10. In the case of the Canadian horseweed or Erigeron canadensis, which is widely naturalized in Europe, the tallest specimens are often twenty-five times as tall as the smallest, the difference increasing to greater extremes, if besides the main stem, the length of the numerous branches of the tall plants are taken into consideration. Other instances studied by the French investigator are Erythraea pulchella and Calamintha Acinos. [454] Dimorphism is of universal occurrence in the whole vegetable kingdom. In some cases it is typical, and may easily be discerned from extreme fluctuating variability. In others the contrast is not at all obvious, and a closer investigation is needed to decide between the two possibilities. Sometimes the adaptive quality is evident, in other cases it is not. A large number of plants bear two kinds of leaves linked with one another by intermediate forms. Often the first leaves of a shoot, or those of accidentally strong shoots, exhibit deviating shapes, and the usefulness of such occurrences seems to be quite doubtful. The elongation of stems and linear leaves, and the reduction of lateral organs in darkness, is manifestly an adaptation. Many plants have stolons with double adaptations which enable them to retain their character of underground stems with bracts or to exchange it for the characteristics of erect stems with green leaves according to the outer circumstances. In some shrubs and trees the capacity of a number of buds to produce either flowers or shoots with leaves seems to be in the same condition. The capacity of producing spines is also a double adaptation, active on dry and arid soil and latent in a moist climate or under cultivation, as with the wild and cultivated apple, and in the experiments of Lothelier [455] with Berberis, Lycium and other species, which lose their spines in damp air. In some conifers the evolution of horizontal branches may be modified by simply turning the buds upside down. Or the lateral branches can be induced to become erect stems by cutting off the normal summit of a tree. Numerous organs and functions lie dormant until aroused by external agencies, and many other cases could be cited, showing the wide occurrence of double adaptation. There are, however, two points, which should not be passed over without some mention. One of them is the influence of sun and shade on leaves, and the other the atavistic forms, often exhibited during the juvenile period. The leaves of many plants, and especially those of some shrubs and trees, have the capacity of adapting themselves either to intense or to diffuse light. On the circumference of the crown of a tree the light is stronger and the leaves a small and thick, with a dense tissue. In the inner parts of the crown the light is weak and the leaves are broader in order to get as much of it as possible. They become larger but thinner, consisting often of a small number of cell layers. The definitive formation is made in extreme youth, often even during the previous summer, at the time of the [456] very first evolution of the young organs within the buds. Iris, and Lactuca Scariola or the prickly lettuce, and many other plants afford similar instances. As the definitive decision must be made in these cases long before the direct influence of the conditions which would make the change useful is felt, it is hardly conceivable how they could be ascribed to this cause. It is universally known that many plants show deviating features when very young, and that these often remind us of the characters of their probable ancestors. Many plants that must have been derived from their nearest systematic relatives, chiefly by reductions, are constantly betraying this relation by a repetition of the ancestral marks during their youth. There can be hardly a doubt that the general law of natural selection prevails in such cases as it does in others. Or stated otherwise, it is very probable, that in most cases the atavistic characters have been retained during youth because of their temporary usefulness. Unfortunately, our knowledge of utility of qualities is as yet, very incomplete. Here we must assume that what is ordinarily spared by natural selection is to be considered as useful, [457] until direct experimental investigations have been made. So it is for instance with the submerged leaves of water-plants. As a rule they are linear, or if compound, are reduced to densely branching filiform threads. Hence we may conclude that this structure is of some use to them. Now two European and some corresponding American species of water-parsnip, the Sium latifolium and Berula angustifolia with their allies, are umbellifers, which bear pinnate instead of bi- or tri-pinnate leaves. But the young plants and even the young shoots when developing from the rootstocks under water comply with the above rule, producing very compound, finely and pectinately dissected leaves. From a systematic point of view these leaves indicate the origin of the water-parsnips from ordinary umbellifers, which generally have bi- and tripinnate leaves. Similar cases of double adaptation, dependent on external conditions at different periods of the evolution of the plant are very numerous. They are most marked among leguminous plants, as shown by the trifoliolate leaves of the thorn-broom and allies, which in the adult state have green twigs destitute of leaves. As an additional instance of dimorphism and probable double adaptation to unrecognized external [458] conditions I might point to the genus Acacia. As we have seen in a previous lecture some of the numerous species of this genus bear bi-pinnate leaves, while others have only flattened leaf-stalks. According to the prevailing systematic conceptions, the last must have been derived from the first by the loss of the blades and the corresponding increase of size and superficial extension of the stalk. In proof of this view they exhibit, as we have described, the ancestral characters in the young plantlets, and this production of bi-pinnate leaves has probably been retained at the period of the corresponding negative mutations, because of some distinct, though still unknown use. Summarizing the results of this discussion, we may state that useful dimorphism, or double adaptation, is a substitution of characters quite analogous to the useless dimorphism of cultivated ever-sporting varieties and the stray occurrence of hereditary monstrosities. The same laws and conditions prevail in both cases.