Note 98 — IDEAS FOR A PHYSIOGNOMY OF PLANTS.

p. 229—“Ferns.”

If we estimate the whole number of the cryptogamia hitherto described at 19,000 species, as has been done by Dr. Klotzsch, a naturalist possessing a profound acquaintance with the Agamic plants, we shall have for Fungi 8000 (of which Agarici constitute the eighth part); for Lichens, according to J. von Flotow of Hirschberg, and Hampe of 338Blankenburg, at least 1400; for the Algæ 2580; for Mosses and Liverworts, according to Carl Müller of Halle, and Dr. Gottsche of Hamburgh, 3800; and for Ferns 3250. For this last important result we are indebted to the profound investigations made by Professor Kunze of Leipzig, on this group of plants. It is a striking fact that the family of the Polypodiaceæ alone includes 2165 of the whole number of described Filices, whilst other forms, as the Lycopodiacæ and Hymenophyllaceæ, number only 350 and 200. There are therefore nearly as many described species among Ferns as among Grasses.

It is singular that no mention of the beautiful arborescent ferns is to be found in the classic authors of antiquity, Theophrastus, Dioscorides, and Pliny; while, from the information given by the companions of Alexander, Aristobulus, Megasthenes, and Nearchus, reference is made^[QM] to Bamboos, “quæ fissis internodiis lembi vice vectitabant navigates;” to the Indian trees “quarum folia non minora clypeo sunt;” to the Fig-tree which takes root from its branches, and to Palms, “tantæ proceritatis, ut sagittis superjici nequeant.” I find the first mention of arborescent ferns in Oviedo.^[QN] “Among ferns,” says this experienced traveller, who had been appointed by Ferdinand the Catholic, Director of the Goldwashings in Haiti, “there are some which I class with trees, because they are as thick and high as Pine-trees. (Helechos que yo cuento por arboles, tan gruesos como grandes pinos y muy altos). They mostly grow among the mountains and where there is much water.” This estimate of their height is exaggerated, for in the dense forests near Caripe even our Cyathea speciosa only attains a height of 32 to 37 feet; and an admirable observer, Ernst Dieffenbach, did not see in the most northern of the three islands of New Zealand any trunks of Cyathea dealbata exceeding 42½ feet. In the Cyathea speciosa and the Meniscium of the Chaymas missions, we observed in the midst of the most shady part of the primeval forest, that the scaly stems of some of the most luxuriantly developed of these trees were covered with a shining carbonaceous powder, which appeared to be owing to a singular decomposition of the fibrous parts of the old leaf stalks.^[QO]

339Between the tropics, where, on the declivities of the Cordilleras, climates are superimposed in strata, the true region of arborescent ferns lies between about 3200 and 5350 feet above the level of the sea. In South America and in the Mexican highlands they seldom descend lower towards the plains than 1280 feet. The mean temperature of this happy region is between 64°.6 and 70°.8 Fahr. It reaches the lowest stratum of clouds (which floats the nearest to the surface of the sea and the plain), and it therefore enjoys uninterruptedly a high degree of humidity, together with a great equality in its thermal relations.^[QP] The inhabitants, who are of Spanish descent, call this region “Tierra templada de los helechos.”

The Arabic designation for ferns is feledschun, filix, (from which the f has been changed, according to Spanish usage, into h,) and perhaps the term may be connected with the verb faladscha, “it divides,” from the finely cut margin of the frond.^[QQ]

The conditions of genial mildness in an atmosphere charged with aqueous vapour and of great uniformity in respect to moisture and warmth, are fulfilled on the declivities of the mountains in the valleys of the Andes, and more especially in the southern milder and more humid hemisphere, where arborescent ferns advance not only to New Zealand and Van Diemen’s Land (Tasmania), but even as far as the Straits of Magellan and Campbell Island, and therefore to a southern latitude almost identical in degrees with the parallel in which Berlin is situated north of the equator. From among the family of arborescent ferns there flourishes the vigorous Dicksonia squarrosa, in 46° south lat. in Dusky Bay, New Zealand; D. antarctica of Labillardière in Tasmania; a Thyrsopteris in the Island of Juan Fernandez; an undescribed Dicksonia, whose stem is from 12 to 16 feet high, near Valdivia in Southern Chili; and a Lomaria, somewhat less in height, in the Straits of Magellan. Campbell Island is still nearer to the south pole, in 52½° lat., but even there the leafless stem of the Aspidium venustum rises to a height of more than four feet.

The climatic relations under which Ferns (Filices) in general flourish, are manifested in the numerical laws of their 340quotients of distribution. In the plains within the tropical regions of large continents this quotient is, according to Robert Brown, and from more recent investigations on the subject, ¹⁄₂₀ of all the phanerogamia, and in mountainous districts of large continents ⅙ to ⅛. This ratio is quite different on the small islands scattered over the ocean; for here the proportion borne by the number of ferns to the sum total of all the phanerogamic plants increases so considerably, that in the South-Sea Islands the quotient rises to ¼, while in the sporadic islands, St. Helena and Ascension, the number of ferns is almost equal to half of the whole phanerogamic vegetation.^[QR] In receding from the tropics (where on the large continents d’Urville estimates the proportional number at ¹⁄₂₀), the relative frequency of ferns decreases rapidly as we advance into the temperate zone. The quotients are for North America and the British Islands ¹⁄₃₅, for France ¹⁄₅₈, for Germany ¹⁄₅₂, for the dry parts of Southern Italy ¹⁄₇₄, for Greece ¹⁄₈₄. The relative frequency again increases considerably towards the frigid north. Here the family of ferns decreases much slower in the number of its species than does that of phanerogamic plants. The luxuriantly aspiring character of the species, and the number of individuals contained in each, augment the deceptive impression of absolute frequency. According to Wahlemberg’s and Hornemann’s catalogues, the relative numbers of the Filices are for Lapland ¹⁄₂₅, for Iceland ¹⁄₁₈, for Greenland ¹⁄₁₂.

Such are, according to our present knowledge, the natural laws that manifest themselves in the distribution of the graceful form of Ferns. But it would seem as if in the family of Ferns, which have so long been regarded as cryptogamic, we had lately acquired evidence of the existence of another natural law,—the morphological law of propagation. Count Leszczyc-Suminski, who happily combines the power of microscopic investigation with a very remarkable artistic talent, has discovered an organisation capable of effecting fructification in the prothallium of ferns. He distinguishes two sexual apparatuses, of which the female portion is situated in hollow ovate cells in the middle of the sporangium, and the male in the ciliated antheridia, or the organs producing spiral threads, which have already been examined by Nägeli. Fructification 341is supposed to be effected by means of moveable ciliated spiral threads and not by pollen tubes.^[QS] According to this view, Ferns would be, as Ehrenberg remarks,^[QT] products of a microscopic fructification taking place on the prothallium, which here serves as a fertilizing receptacle, while throughout the whole course of their often arborescent development they would be flowerless and fruitless plants, having a bud-formation. The spores lying as sori on the under side of the frond are not seeds but flower-buds.