Sub-Division III. FUNGI.

Mode of Life. The Fungi have no chlorophyll, and are thus unable in any stage of their existence to assimilate carbon; they must therefore live as saprophytes or parasites. There is, however, no strong line of demarcation between these; many Fungi commence as true parasites, but only attain their full development upon or in dead plants or animals (Rhytisma, Empusa). Many saprophytes may occasionally appear as parasites, and are then designated “facultative parasites” (Nectria cinnabarina, Lophodermium pinastri), in contradistinction to those which only appear as parasites, “obligate parasites” (Mildew, Brand-and Rust-Fungi, Cordyceps).

The parasites which live on the surface of the host-plant are termed epiphytic (Mildew, Fusicladium); and those living in its tissues are termed endophytic (Ustilago, Peronospora). Epizoic (Oidium tonsurans, Laboulbenia) and endozoic Fungi (Cordyceps, Entomophthora), are distinguished, in the same manner, as those which live on the surface or in the interior of animals. The Fungi designated pathogenic are especially those which produce disease in human beings and in animals.

Most of the diseases of plants are attributed to the parasitic Fungi. These force their way into the host-plant by piercing the outer wall of the epidermis, as in the Potato-disease; or by growing in through the stomata, e.g. the summer generations of the Rust of Wheat; or they can only penetrate through a wound, e.g. Nectria. Some effect an entrance into the host-plant by the secretion of a poisonous matter or ferment, which softens and destroys the cell-walls (Sclerotinia). Some Yeast and Mould Fungi secrete ferments (enzymes), which, for example, convert cane-sugar into a sugar capable of fermentation.

The relation of the parasitic Fungus to the host-plant is mainly of two kinds. In the one case, the cell-contents are destroyed, the protoplasm is killed, and the cellular tissue becomes discoloured and dies (Peronospora, Armillaria mellea, Polyporus); in the other case, the parasite has an irritating effect on the cellular tissue, whereby the affected organ grows more rapidly and becomes larger than normal, producing hypertrophy. Such malformations are termed Fungi-galls (Mycocecidia); in this manner “witches’ brooms” are produced by Æcidium, “pocket-plum” by Taphrina, and other deformities by Exobasidium and Cystopus candidus. This hypertrophy may either be produced by a vigorous cell-multiplication, which is most frequently the case, or by the enlargement of the individual cells (Synchytrium, Calyptospora). The relation between host and Fungus among the Lichens is of a very peculiar nature, termed “symbiosis.”

Vegetative Organs. The vegetative parts of a Fungus are termed its mycelium.[10] This is formed of a mass of long, cylindrical, branched cells resembling threads (and hence termed hyphæ), which have a continued apical growth. The mycelium, in its early development, shows a well-marked difference between the two main groups of true Fungi: in the Phycomycetes, or Algal Fungi, the mycelium has no transverse walls, and is therefore unicellular, while in the Mesomycetes and Mycomycetes it is provided with dividing walls, which gradually arise during growth, in the youngest hyphæ; intercalary transverse walls may also be formed at a later period. In the hyphæ of some of the Higher Fungi (Hymenomycetes), connections may be formed between two contiguous cells of the same hypha, by a protuberance growing out from an upper cell just above the transverse wall, and forming a junction with the cell below. These are known as clamp-connections; they appear to be of use in affording communication between the two cells.

The hyphæ of Fungi, where they come in contact with one another, often grow together, so that H-formed combinations (fusions) are produced, which give rise to very compact felted tissue. When the hyphæ are not only closely interwoven, but also united and provided with many transverse walls, the mycelium assumes the appearance of a tissue with isodiametric cells, and is then termed pseudo-parenchyma. The hyphæ-walls are sometimes very much thickened, and composed of several layers, and the external layers, by the absorption of water, may often swell very much and become mucilaginous. In some instances the walls are colourless, in others coloured, the most frequent colour being brown. The cell-contents may also be coloured, and in that case are generally yellow; this colour is chiefly connected with the fat (oil) which may be found in abundance in the Fungi, whilst starch is invariably absent in all the true Fungi.

The mycelium assumes many different forms; sometimes it appears as a thread-like, cobwebby, loose tissue, less frequently as firm strands, thin or thick membranes, horn-like plates or tuber-like bodies. The thread-like mycelium may, in the parasitic Fungi, be intercellular or intracellular, according as it only extends into the interstices between the cells or enters into the cells proper. In the first case there are generally found haustoria, or organs of suction (e.g. among the Peronosporaceæ; Taphrina, on the contrary, has no haustoria); but haustoria are also found among the epiphytic Fungi (e.g. Erysiphaceæ). Intracellular mycelia are found in the Rust-Fungi, in Claviceps purpurea, Entomophthora, etc. In spite of its delicate structure, this mycelium may live a long time, owing to the circumstance that it continues to grow peripherally, while the older parts gradually die off (“fairy rings”).

String-like mycelia may be found, for example, in Phallus, Coprinus, and are formed of hyphæ, which run more or less parallel to each other. Membrane-like mycelia are chiefly to be found in Fungi growing on tree-stems (Polyporaceæ and Agaricaceæ); they may have a thickness varying from that of the finest tissue-paper to that of thick leather, and may extend for several feet. The peculiar horny or leather-like strands and plates which, for instance, appear in Armillaria mellea, are known as Rhizomorpha; they may attain a length of more than fifty feet. The tuber-like mycelia or sclerotia play the part of resting mycelia, since a store of nourishment is accumulated in them, and after a period of rest they develope organs of reproduction. The sclerotia are hard, spherical, or irregular bodies, from the size of a cabbage seed to that of a hand, internally white or greyish, with a brown or black, pseudo-parenchymatous, external layer. Sclerotia only occur in the higher Fungi, and are found both in saprophytes, e.g. Coprinus, and in parasites, e.g. Claviceps (Ergot), Sclerotinia.

Reproduction. Sexual reproduction is found only among the lower Fungi which stand near to the Algæ, the Algal-Fungi, and takes place by the same two methods as in the Algæ, namely by conjugation and by the fertilisation of the egg-cell in the oogonium.

The majority of Fungi have only ASEXUAL reproduction. The most important methods of this kind of reproduction are the sporangio-fructification and the conidio-fructification.

In the SPORANGIO-FRUCTIFICATION the spores (endospores) arise inside a mother-cell, the sporangium (Fig. 80). Spores without a cell-wall, which move in water by means of cilia and hence are known as swarmspores or zoospores, are found among the Oomycetes, the sporangia in which these are produced being called swarm-sporangia or zoosporangia (Figs. 86, 87, 91, 94).

In the CONIDIO-FRUCTIFICATION the conidia (exospores) arise on special hyphæ (conidiophores), or directly from the mycelium. When conidiophores are present, the conidia are developed upon them terminally or laterally, either in a basipetal succession (in many Fungi, for example in Penicillium, Fig. 111, Erysiphe, Cystopus), or acropetally (in which method the chains of conidia are often branched; examples, Pleospora vulgaris, Hormodendron cladosporioides). All conidia are at first unicellular, sometimes at a later stage they become two-celled or multicellular through the formation of partition-walls (Piptocephalis). The conidia with thick, brown cell-walls, and contents rich in fats (resting conidia), can withstand unfavourable external conditions for a much longer period than conidia with thin walls and poor in contents.

The SPORANGIA arise either from the ordinary cells of the mycelium (Protomyces), or are borne on special hyphæ. They are generally spherical (Mucor, Fig. 80; Saprolegniaceæ), egg-, pear-, or club-shaped (Ascomycetes), more rarely they are cylindrical or spindle-shaped. While among the Phycomycetes the size, form, and number of spores are indefinite in each species, in the Ascomycetes the sporangia (asci) have a definite size, form, and number of spores. The spores of the Ascomycetes are known as ascospores.

The sporangio-fructification is found under three main forms.

1. Free Sporangiophores which are either single (Mucor, Fig. 78), or branched (Thamnidium).

2. Sporangial-layers. These are produced by a number of sessile or shortly-stalked sporangia, being formed close together like a palisade (Taphrina, Fig. 105).

3. Sporangiocarps. These consist usually of many sporangia enclosed in a covering, they are found only in the Carpoasci, and are also known as ascocarps. The parts of an ascocarp are the covering (peridium), and the hymenium, which is in contact with the inner wall of the peridium, and is generally made up of asci, and sterile, slender hyphæ. The latter either penetrate between the asci and are branched and multicellular (paraphyses, Figs. 103 d, 123, 125, 129), or clothe those parts of the inner wall which bear no asci (periphyses; among many peronocarpic Ascomycetes, e.g. Chætomium, Sordaria, Stictosphæra hoffmanni). The ascocarps are produced directly from the mycelium, or from a stroma, that is a vegetative body of various forms, in which they may be embedded (Figs. 116 B, C).

Among the conidio-fructifications there are, in the same way, three divisions.

1. Free conidiophores (Fig. 109). The form of the conidiophores, the shape, and number of its spores are various. In the most highly developed Fungi, the Basidiomycetes, there are, however, special more highly developed conidiophores, the basidia, which have a definite form and spores of a definite shape and number. The conidia borne on basidia are called basidiospores.

2. Conidial-layers. (a) The SIMPLEST case of this is found when the conidiophores arise directly from the mycelium, parallel to one another, and form a flat body (e.g. Exobasidium vaccinii, Hypochnus; among the Phycomycetes, Empusa muscæ and Cystopus). (b) In a HIGHER form the conidial-layers are thick, felted threads (stroma) inserted between the mycelium and the hymenium (i.e. the region of the conidiophores). Examples are found in a section of the Pyrenomycetes (Fig. 122). (c) The HIGHEST form has the basidial-layer, that is a conidial-layer with more highly developed conidiophores (basidia). The basidial-layer, with stroma, and the hymenium (region of the basidia), forms the basidio-fructification, which is branched in the Clavariaceæ, and hat-shaped in other Hymenomycetes (in these groups the hymenium is confined to the lower side of the pileus).

The hymenium of the conidial-layer and basidial-layer is composed entirely of conidiophores, or of conidiophores and sterile hyphæ (paraphyses) which are probably always unicellular. Paraphyses are found in Entomophthora radicans, and in certain Basidiomycetes (e.g. Corticium).

3. Conidiocarps (pycnidia). A special covering surrounds the conidia-forming elements. The inner side of this covering (peridium) bears the hymenium, i.e. those elements from which the conidia are abstricted. The conidiocarps arise either immediately from the hyphæ or from a stroma in which they are generally embedded. Conidiocarps are entirely wanting in the Phycomycetes. On the other hand they are found among the Ascomycetes and Basidiomycetes, and in the latter group the conidiocarps contain more highly differentiated conidiophores (basidia) and are known as basidiocarps. Conidiocarps with simple conidiophores, are found only among the Basidiomycetes, in the Uredinaceæ, and in Craterocolla cerasi. In the Ascomycetes (Figs. 120 d, e; 117 a, b; 123 a; 124 b) the conidiocarps are visible, as points, to the naked eye, while the basidiocarps of the Basidiomycetes (Figs. 170, 171, 173–176, 178–180) vary from the size of a pea to that of a child’s head. The “spermogonia” of the Ascomycetes and Lichenes, are conidiocarps with small conidia (microconidia) which germinate sometimes more slowly than other conidia, and formerly were erroneously considered as male reproductive cells, and called spermatia.

The conidia of the Fungi are not primitive structures. The comparison of the sporangia and conidia among the Zygomycetes, and among the species of the genus Peronospora shows, that the conidia are aberrant formations, and that they have arisen through the degeneration of the sporangium, which, by the reduction of its spores to one, has itself become a spore.

In the genera Thamnidium and Chætocladium the gradual diminution of the sporangia, and the reduction of the number of spores can be distinctly followed. In Thamnidium the number of spores is often reduced to one, which is free in the sporangium. In Chætocladium however the sporangia are typically one-spored, the spore is always united with the sporangium, and the two become a single body, the so-called conidium, which is in reality a closed sporangium. How close is the connection between the sporangia and conidia of Thamnidium and Chætocladium, is seen from the fact that, in the conidial stage of Chætocladium the same whorl-form of branching appears as in the sporangial stages of Thamnidium chætocladioides, and also, that the conidia of Ch. fresenianum throw off the former sporangium-wall (exosporium), while Ch. jonesii germinates without shedding its exosporium. The Phycomycetes have doubtless sprung from Water-Algæ and inherit the sporangia from them. On this supposition, as the Phycomycetes assumed a terrestrial mode of life, the sporangia would become adapted to the distribution of the spores by means of the air, the sporangia would become small, contain dust-like spores, and would eventually become closed-sporangia, i.e. conidia. The conidia are a terrestrial method for the multiplication of Fungi. In the Hemiasci and the Ascomycetes the sporangia are still preserved, but in every instance they are adapted to terrestrial spore-distribution, their spores being set free on the destruction of the sporangium-wall (generally shot out) and distributed through the air. For further examples of spore-distribution see below, p. 91–93.

The reproduction of Fungi is accomplished not only by spores and conidia, but also sometimes by chlamydospores. These are fundaments[11] of sporangiophores and conidiophores, which have taken on a resting condition in the form of a spore, and are able to germinate and produce carpophores. In the formation of the chlamydospores the hyphæ accumulate reserve materials at the expense of the neighbouring cells; in the undivided hyphæ of the Phycomycetes transverse walls are formed, and finally the chlamydospores are set free by the decay of the empty cells connecting them with the mycelium. One must distinguish between oidia and true chlamydospores. The former are more simple, the latter are a somewhat more differentiated form of carpophore fundaments, which serve for propagation in the same manner as spores. In Chlamydomucor racemosus the chlamydospores grow out into the air and form differentiated carpophores. In the Autobasidiomycetes they only germinate vegetatively, and not with the formation of fructifications. From Chlamydomucor up to the Autobasidiomycetes the successive development of the fructification, which is interrupted by the formation of the chlamydospores, degenerates more and more. Among certain Ustilagineæ the chlamydospores (brand-spores) no longer germinate with the production of fructifications. In the Uredinaceæ, only one of the three chlamydospore-forms has the property of producing fructifications on germination; the other forms only germinate vegetatively, like ordinary spores, and in the same manner as the chlamydospores of the Autobasidiomycetes. In the Hemibasidii, and the Uredinaceæ, in Protomyces, the chlamydospores are the chief means of reproduction. They are found also among the Ascomycetes.

The sporangia and the conidia of the Fungi have their common origin in the sporangia of the Phycomycetes. The asci (and the Ascomycetes which are characterised by these bodies) are descended from the sporangia-forming, lower Fungi; the basidia (and the Basidiomycetes) from those which bear conidia. The sporangia of the Phycomycetes are the primitive form and the starting point for all the reproductive forms of the Fungi. The chlamydospores appear besides in all classes of Fungi as supplementary forms of reproduction, and are of no importance in determining relationships. Although the expression “fruit” must essentially be applied to true Phanerogams, yet, through usage, the term “fruit-forms,” is employed to designate the forms or means of reproduction of Fungi, and the organs of reproduction are known as organs of fructification, the sporangiophores and conidiophores as fruit-bearers (carpophores), and the sporangiocarps, conidiocarps, and basidiocarps as “fruit-bodies.”

The majority of Fungi have more than one method of reproduction, often on various hosts (Uredinaceæ). Species with one, two, or more than two methods of reproduction are spoken of as having monomorphic, dimorphic, or pleomorphic fructification. Monomorphic, e.g. the Tuberaceæ; dimorphic, Mucor, Piptocephalis, Saprolegniaceæ, Penicillium crustaceum; pleomorphic, Puccinia graminis, Capnodium salicinum (in the last species there are five methods of reproduction: yeast-like conidia, free conidiophores, conidiocarps with small and large conidia, and ascocarps).

The liberation and distribution of the spores and conidia. The spores and conidia, on account of their small size and lightness, are spread far and wide by currents in the air, but in addition to this method, insects and other animals frequently assist in disseminating them. The liberation of the conidia is occasionally effected by the complete shrinking away of the conidiophore, but more frequently by abstriction from the conidiophores, either by their gradually tapering to a point, or by the dissolution of a cross-wall (generally of a mucilaginous nature). The individual links of conidia-chains are detached from one another in the same way, or often by means of small, intercalary cells, which are formed at the base of the individual links, and becoming slimy, dissolve upon the maturity of the spores. Special contrivances for ejecting the spores and conidia may often be found. In Peronospora the cylindrical fruit-hyphæ in the dry condition become strap-shaped and also twisted. These are very hygroscopic, and the changes of form take place so suddenly, that the spores are violently detached and shot away. In Empusa a peculiar squirting mechanism may be found (Fig. 85). Each club-shaped hypha which projects from the body of the fly, bears a conidium at its apex; a vacuole, which grows gradually larger, is formed in the slimy contents of the hypha, and the pressure thereby eventually becomes so great that the hypha bursts at its apex, and the conidium is shot into the air. By a similar mechanism, the spores of many of the Agaricaceæ are cast away from the parent-plants. In the case of Pilobolus (Fig. 84) the entire sporangium is thrown for some distance into the air by a similar contrivance, the basal region of the sporangium having, by the absorption of water, been transformed into a slimy layer which is readily detached. Sphærobolus, a Gasteromycete, has a small, spherical fruit-body (basidiocarp), the covering of which, when ripe, suddenly bursts, and the basidiospores contained in it are forcibly ejected.

The spores which are enclosed in asci are, in some instances, set free from the mother-cell (ascus) prior to their complete development (Elaphomyces, Eurotium). In the case of the majority of the Pyrenomycetes and Truffles, the asci swell by the absorption of water into a slimy mass, which gradually disappears, so that the spores lie free in the fruit-body; they either remain there till the fruit-body decays, as in those which have no aperture (Perisporiaceæ, Tuberaceæ), or the slimy mass, by its growth, is forced out through the aperture of the sporocarp, taking the spores with it (Nectria). The ejection of the spores by mechanical means takes place in a number of Ascomycetes, and should many spores be simultaneously ejected, a dust-cloud may be seen with the naked eye to arise in the air from the fruit-body. This is the case in the larger species of Peziza, Helvella, Rhytisma, when suddenly exposed to a damp current of air. A distinction is drawn between a simultaneous ejection of all the spores contained in the ascus, and an ejection at intervals (successive), when only one spore at a time is thrown out. The first of these methods is the most frequent, and is brought about by the ascus being lined with a layer of protoplasm, which absorbs water to such a degree that the elastic walls are extended at times to double their original size. The spores are forced up against the free end of the ascus, a circular rupture is made at this point, and the elastic walls contract, so that the fluid with the spores is ejected. Special means may in some instances be found to keep the spores together, and compel their simultaneous ejection. Thus, a tough slime may surround all the spores (Saccobolus), or a chain-apparatus, similarly formed of tough slime; or there may be a hooked appendage from each end of the spores which hooks into the appendage of the next spore (Sordaria). The paraphyses occurring between the asci in many Ascomycetes, also play a part in the distribution of the spores, by reason of the pressure they exercise. The asci in some of the Pyrenomycetes, which are provided with jar-shaped fruit-bodies, elongate to such an extent that, without becoming detached from their bases, they reach the mouth of the fruit-body one at a time, burst and disperse their spores, and so make room for those succeeding. An ejection of the spores at intervals from the ascus is rarer. It takes place, for instance, in Pleospora, whose asci have a double wall. The external wall, by absorption of water, at last becomes ruptured, and the internal and more elastic membrane forces itself out in the course of a few seconds to one of two or three times greater length and thickness, so that one spore after another is forcibly ejected from a narrow aperture at the end of the ascus.

Germination of spores (conidia and chlamydospores). In many spores may be found one or more germ-pores, i.e. thinner places, either in the inner membrane (uredospores, Sordaria) or in the external membrane (teleutospores in Rust-Fungi), through which the germination takes place. Generally this does not occur till the spores have been set free: in some Ascomycetes germination commences inside the ascus (Taphrina, Sclerotinia). The different ways in which the spores germinate may be classified into three groups.

I. The ordinary germination occurs by the spore emitting a germ-tube, which immediately developes into a mycelium. In spores with a double wall it is only the inner membrane which forms the germ-tube. In swarmspores a single wall is formed after the withdrawal of the cilia, and this, by direct elongation, becomes the germ-tube. The protoplasm accumulated in the spore enters the hypha, which, in pure water, can only grow as long as the reserve nourishment lasts.

2. Germination with promycelium differs only by the circumstance that the hypha developed from the germ-tube has a very limited growth, and hence it does not immediately develope into a mycelium, but produces conidia (Rust-and Brand-Fungi). This promycelium must only be regarded as an advanced development of a conidiophore or basidium.

3. The yeast-formation of conidia consists in the production of outgrowths, very much constricted at their bases, from one or more places. Each of the conidia formed in this manner may again germinate in the same way. When sufficient nourishment is present, a branched chain of such conidia is formed, and these are finally detached from one another. Yeast-like buddings from the conidia are produced in various Fungi, e.g. Ascoidea, Protomyces, Ustilagineæ, Ascomycetes, Tremellaceæ, etc. In the Ustilagineæ these conidia are an important element in the development. The budding conidia of Exobasidium forms a “mould” on the nutritive solution. The yeast-like conidia are not to be confounded with the “Mucor-yeast” (comp. Mucoraceæ). For Saccharomyces see Appendix to the Fungi, page 176.

In a compound spore (i.e. when a mass of spores are associated together) each spore germinates on its own account. There are sometimes, however, certain among them which do not germinate, but yield their contents to those which do.

The length of time for which conidia can retain their power of germination is shortest (being only a few weeks) in those having thin walls and containing a large supply of water (Peronosporaceæ, Uredinaceæ). In many spores a resting period is absolutely necessary before they are able to germinate (resting spores). It has been observed in some spores and conidia, that the faculty of germinating may be preserved for several years if the conditions necessary for germination remain absent (Ustilagineæ, Eurotium, Penicillium).

The optimum, minimum and maximum temperatures required for the germination of the spores has been decided in the case of a good many Fungi. A large portion of the most common Fungi have their optimum at 20°C., minimum at 1–2°C, maximum at 40°C. In the case of pathogenic Fungi the optimum is adapted to the temperature of the blood. Fungi living in manure, whose spores are often adapted to germinate in the alimentary canals of warm-blooded animals, have an optimum corresponding to the temperature of these animals, but with a little margin.

Systematic Division.—The lowest class of the Fungi is that of the Phycomycetes, which have an unicellular mycelium, sexual and asexual reproduction, and have doubtless sprung from sporangia-bearing, lower Green Algæ. From the Phycomycetes (and certainly from the Zygomycetes) spring two well defined branches, each with numerous distinct species; to the one branch belong the Hemiasci and the Ascomycetes, to the other the Hemibasidii and the BASIDIOMYCETES. Ascomycetes and Basidiomycetes may be united under the title of Mycomycetes or Higher Fungi. The Hemiasci and the Hemibasidii constitute the class of Mesomycetes. The Hemiasci are an intermediate form between Zygomycetes and Ascomycetes; the Hemibasidii a similar group between the Zygomycetes and Basidiomycetes. Mesomycetes and Mycomycetes have only asexual reproduction; sexual reproduction is wanting. Their mycelium is multicellular.

Up to the present time about 39,000 species have been described.

Review of the divisions of the Fungi:—

Class I.—Phycomycetes (Algal-Fungi).

Sub-Class 1. Zygomycetes.

Sub-Class 2. Oomycetes.

Family 1. Entomophthorales.

Family 2. Chytridiales.

Family 3. Mycosiphonales.

Class II. Mesomycetes.

Sub-Class 1. Hemiasci.

Sub-Class 2. Hemibasidii (Brand-Fungi).

Class III.—Mycomycetes (Higher Fungi).

Sub-Class 1. Ascomycetes.

Series 1. Exoasci.

Series 2. Carpoasci.

Family 1. Gymnoascales. }

Family 2. Perisporiales. }Angiocarpic Exoasci.

Family 3. Pyrenomycetes. }

Family 4. Hysteriales. }

Family 5. Discomycetes. } Hemiangiocarpic Exoasci.

Family 6. Helvellales. Gymnocarpic (?) Exoasci.

Additional: Ascolichenes. Lichen-forming Ascomycetes.

Sub-Class 2. Basidiomycetes.

Series 1.—Protobasidiomycetes. Partly gymnocarpic, partly angiocarpic.

Series 2. Autobasidiomycetes.

Family 1. Dacryomycetes. Gymnocarpic.

Family 2. Hymenomycetes. Partly gymnocarpic, partly hemiangiocarpic.

Family 3. Phalloideæ. Hemiangiocarpic.

Family 4. Gasteromycetes. Angiocarpic.

Additional: Basidiolichenes. Lichen-forming Basidiomycetes.

Additional to the Fungi: Fungi Imperfecti. Incompletely known (Saccharomyces, Oidium-forms, etc.).

Class 1. Phycomycetes (Algal-Fungi).[12]

This group resembles Vaucheria and the other Siphoneæ among the Algæ.

Organs of Nutrition. The mycelium is formed of a single cell, often thread-like and abundantly branched (Fig. 78). Vegetative propagation by chlamydospores and oidia. Asexual reproduction by endospores (sometimes swarmspores) and conidia. Sexual reproduction by conjugation of two hyphæ as in the Conjugatæ, or by fertilisation of an egg-cell in an oogonium. On this account the class of the Phycomycetes is divided into two sub-classes: Zygomycetes and Oomycetes.

Sub-Class I. Zygomycetes.

Sexual reproduction takes place by zygospores, which function as resting-spores, and arise in consequence of conjugation (Fig. 81); in the majority of species these are rarely found, and only under special conditions. The most common method of reproduction is by endospores, by acrogenous conidia, by chlamydospores, or by oidia. Swarmspores are wanting. Parasites and saprophytes (order 6 and 7). The zygospores are generally produced when the formation of sporangia has ceased; e.g. by the suppression of the sporangial-hyphæ (Mucor mucedo), or by the diminution of oxygen; Pilobolus crystallinus forms zygospores, when the sporangia are infected with saprophytic Piptocephalis or Pleotrachelus.

A. Asexual reproduction only by sporangia.

Order 1. Mucoraceæ. The spherical sporangia contain many spores. The zygospore is formed between two unicellular branches (gametes).

The unicellular mycelium (Fig. 78) of the Mucoraceæ branches abundantly, and lives, generally, as a saprophyte on all sorts of dead organic remains. Some of these Fungi are known to be capable of producing alcoholic fermentation, in common with the Saccharomyces. This applies especially to Chlamydomucor racemosus (Mucor racemosus), when grown in a saccharine solution, and deprived of oxygen; the mycelium, under such conditions, becomes divided by transverse walls into a large number of small cells. Many of these swell out into spherical or club-shaped cells, and when detached from one another become chlamydospores, which abstrict new cells of similar nature (Fig. 79). These chlamydospores were formerly erroneously termed “mucor-yeast,” but they must not be confounded with the yeast-conidia (page 94). They are shortened hyphæ, and are not conidia of definite size, shape, and point of budding. Oidia are also found in Chlamydomucor.

Fig. 78.—Mucor mucedo. A mycelium which has sprung from one spore, whose position is marked by the *: a, b, c are three sporangia in different stages of development; a is the youngest one, as yet only a short, thick, erect branch; b is commencing to form a sporangium which is larger in c, but not yet separated from its stalk.

The Mucoraceæ, in addition to the chlamydospores and oidia, have a more normal and ordinary method of reproduction; viz., by spores which are formed without any sexual act. Mucor has round sporangia; from the mycelium one or more long branches, sometimes several centimetres in length, grow vertically into the air; the apex swells (Figs. 78, 80) into a sphere which soon becomes separated from its stalk by a transverse wall; in the interior of this sphere (sporangium) a number of spores are formed which eventually are set free by the rupture of the wall. The transverse wall protrudes into the sporangium and forms the well-known columella (Fig. 80 d, e). The formation of spores takes place in various ways among the different genera.

Fig. 79.—Chlamydospores of Chlamydomucor racemosus (× 375 times.)

Fig. 80.—Mucor mucedo: a a spore commencing to germinate (× 300 times); b a germinating spore which has formed a germ-tube from each end (× 300 times); c the apex of a young sporangium before the formation of spores has commenced; the stalk is protruded in the sporangium in the form of a column: on the wall of the sporangium is found a very fine incrustation of lime in the form of thorn-like projections; d a sporangium in which the formation of spores has commenced; e a sporangium, the wall of which is ruptured, leaving a remnant attached to the base of the columella as a small collar. A few spores are seen still adhering to the columella.

Sexual Reproduction by conjugation takes place in the following manner. The ends of two hyphæ meet (Fig. 81) and become more or less club-shaped; the ends of each of these are cut off by a cell-wall, and two new small cells (Fig. 81 A) are thus formed, these coalesce and give rise to a new cell which becomes the very thick-walled zygote (zygospore), and germinates after period of rest, producing a new hypha, which bears a sporangium (Fig. 81 E).

Mucor mucedo, Pin-mould, resembles somewhat in appearance Penicillium crustaceum and is found growing upon various organic materials (bread, jam, dung, etc.).

Pilobolus (Figs. 83, 84) grows on manure. Its sporangium (Fig. 84 a″) is formed during the night and by a peculiar mechanism (page 92) is shot away from the plant in the course of the day. This generally takes place in the summer, between eight and ten a.m. The sporangium is shot away to a height which may be 300 times greater than that of the plant itself, and by its stickiness it becomes attached to portions of plants, etc., which are in the vicinity. If these are eaten by animals, the spores pass into the alimentary canal and are later on, sometimes even in a germinating condition, passed out with the excrement, in which they form new mycelia.

Phycomyces nitens (“Oil-mould”) is the largest of the Mould Fungi; its sporangiophores may attain the height of 10–30 c.m.

Order 2. Rhizopaceæ. Rhizopus nigricans (Mucor stolonifer) which lives on decaying fruits containing sugar, on bread, etc., has, at the base of the sporangiophores, tufts of rhizoids, i.e. hyphæ, which function as organs of attachment. From these, “runners” are produced which in a similar manner develope sporangiophores and rhizoids.

Figs. 81, 82.—Mucor mucedo: A-C stages in the formation of the zygote; D zygote; E germination of zygote: the exospore has burst, and the endospore grown into a hypha bearing a sporangium.

Order 3. Thamnidiaceæ. On the same sporangiophore, in addition to a large, terminal, many-spored sporangium, many smaller, lateral sporangia are formed with a few spores. Thamnidium.

B. Asexual reproduction by sporangia and conidia.

Order 4. Choanephoraceæ. Choanephora with creeping endophytic mycelium, and perpendicular sporangiophores.

Order 5. Mortierellaceæ. Mortierella polycephala produces on the same mycelium conidia and sporangiophores. M. rostafinskii has a long stalked sporangiophore, which is surrounded at its base by a covering of numerous felted hyphæ.

Fig. 83.—Pilobolus. Mycelium (a, a), with a sporangiophore (A) and the fundament of another (B).

Fig. 84.—Pilobolus. Sporangium (a″) with stalk (a-c), which is covered by many small drops of water pressed out by turgescence.

C. Asexual reproduction only by conidia.

Order 6. Chætocladiaceæ. The conidia are abstricted singly and acrogenously. Chætocladium is a parasite on the larger Mucoraceæ.

Order 7. Piptocephalidaceæ. The conidia are formed acrogenously and in a series, by transverse divisions. The zygospore arises at the summit of the conjugating hyphæ, which are curved so as to resemble a pair of tongs. Piptocephalis and Syncephalis live parasitically on the larger Mucoraceæ.

Sub-Class 2. Oomycetes.

Sexual reproduction is oogamous with the formation of brown, thick-walled oospores which germinate after a period of rest. Asexual reproduction by conidia and swarmspores. Parasites, seldom saprophytes.

The oospores are large spores which are formed from the egg-cell (oosphere) of the oogonium (oosporangium, Fig. 89, 95). A branch of the mycelium attaches itself to the oogonium and forms at its apex the so-called “antheridium” (pollinodium[13]): this sends one or more slender prolongations (fertilising tubes) through the wall of the oogonium to the egg-cell.

Fig. 85.—Empusa muscæ (Fly-mould). I. A fly killed by the fungus, surrounded by a white layer of conidia. II. The conidiophores (t) projecting from the body of the fly. Some of the conidia, a few of which have developed secondary conidia, are attached to the hairs (mag. 80 times). III. A perfect hypha. IV. A hypha in the act of ejecting a conidium (c), enveloped in a sticky slime (g). V. A conidium which has developed a secondary conidium (sc). VI. A branched hypha produced by cultivation. VII. A secondary conidium which has produced a small mycelium (m). VIII. A conidium germinating on the fly’s body. IX. Mycelium. X. Conidia germinating like yeast in the fatty tissue of the fly. (III.-VII. and IX. magnified 300 times; VIII. and X. magnified 500 times.)

A fertilisation, a passage of the contents of the antheridium to the egg-cell, has as yet only been observed in Pythium; in Phytophthora only one small mass of protoplasm passes through the fertilising tube to the egg-cell; in Peronospora and the Saprolegniaceæ no protoplasm can be observed to pass through the fertilising tube, so that in these instances parthenogenesis takes place; Saprolegnia thuretii, etc., have generally even no antheridia, but nevertheless form normal oospores. Fertilisation of the egg-cell by means of self-motile spermatozoids is only found in Monoblepharis sphærica.

A. Asexual reproduction by conidia only.

Family 1. Entomophthorales.

The mycelium is richly branched. The family is a transitional step to the conidia-bearing Zygomycetes, since the oospores of many members of this family arise, and are formed, like zygospores.

Order 1. Entomophthoraceæ. Mycelium abundantly developed. This most frequently lives parasitically in living insects, causing their death. The conidiophores forming the conidial-layer project from the skin, and abstrict a proportionately large conidium which is ejected with considerable force, and by this means transferred to other insects. These become infected by the entrance of the germ-tube into their bodies. The spherical, brown resting-spores develope inside the bodies of insects and germinate by emitting a germ-tube.

Genera: Empusa has a good many species which are parasitic on flies, moths, grasshoppers, plant-lice. The conidia emit a germ-tube which pierces the skin of the insect; a number of secondary conidia are then produced inside its body, by division or by gemmation similar to that taking place in yeast, each of which grows and becomes a long unbranched hypha, and these eventually fill up the body of the animal, causing distension and death. Each of these hyphæ projects through the skin, and abstricts a conidium, which is ejected by a squirting contrivance. The best known species is E. muscæ (Fig. 85), which makes its appearance epidemically towards autumn on the common house-fly, and shows itself by the dead flies which are found on the windows and walls attached by their probosces, distended wings, and legs. They have swollen abdomen, broad white belts of hyphæ between the abdominal rings, and are surrounded by a circle of whitish dust formed by the ejected conidia.—Entomophthora sends out, at definite places, from the mycelium hidden in the insect’s body, bundles of hyphæ, which serve the purpose of holding fast the dead insects, the ramifications attaching themselves to the substratum: the conidiophores are branched, the conidia are ejected by the divisional walls between the hyphæ and the conidia dividing into two layers, those which terminate the hyphæ suddenly expanding and throwing the conidia into the air. E. radicans makes its appearance epidemically on caterpillars.

B. Asexual reproduction by zoospores or conidia.

Family 2. Chytridiales.

In this family the mycelium is very sparsely developed or is wanting. The entire plant consists principally or entirely of a single zoosporangium whose zoospores have generally one cilium. The resting-spores arise either directly from the zoosporangium, which, instead of forming zoospores, surrounds itself by a thick cell-wall; or they are formed by the conjugation of two cells (in which case they are spoken of as oospores). Microscopic Fungi, parasitic on water plants (especially Algæ) or small aquatic animals, seldom on land plants.

Order 1. Olpidiaceæ. Without mycelium. Swarmspores and resting-spores.

In the Olpidieæ, the swarmspores, probably, most frequently form themselves into a plasmodium (naked mass of protoplasm) which may become a single zoosporangium or a resting sporangium. Olpidium trifolii occurs in Trifolium repens.—In the Synchytrieæ the plasmodium emerging from the swarmspores breaks up either at once, or after a period of rest, into smaller plasmodia, each of which will become a zoosporangium. Synchytrium anemones is found on Anemone nemorosa; S. mercurialis on Mercurialis perennis; S. aureum on many plants, particularly Lysimachia nummularia.

Fig. 86.—Chytridium lagenula. Zoosporangium a before, b after the liberation of the swarmspores.

Fig. 87.—Obelidium mucronatum: m mycelium; s swarmspores.

Order 2. Rhizidiaceæ. Mycelium present. Zoospores and resting-spores.

Chytridium (Fig. 86). Obelidium (Fig. 87) is bicellular; the one cell is the mycelium, the other the zoosporangium; found on insects. The species of Cladochytrium are intercellular parasites on marsh plants. Physoderma.

Order 3. Zygochytriaceæ. Mycelium present. Zoospores and oospores. The latter are the product of the conjugation of two cells (Fig. 88).

Polyphagus euglenæ on Euglena viridis. Urophlyctis pulposa on species of Chenopodium.

Family 3. Mycosiphonales.

The mycelium is bladder-like or branched. Zoospores. Sexual reproduction by oospores, which are produced in oogonia. The latter are fertilised, in some forms, by the antheridium.

Order 1. Ancylistaceæ. The entire bladder-like mycelium is used for the construction of zoosporangia, oogonia, or antheridia. Lagenedium is parasitic on Spirogyra, etc.

Order 2. Peronosporaceæ. Almost entirely parasites. The unicellular, often very long and abundantly branched mycelium lives in the intercellular spaces of living plants, especially in the green portions, and these are more or less destroyed and deformed in consequence. Special small branches (suction-organs, “haustoria”) are pushed into the cells in order to abstract nourishment from them. Both oospores and conidia germinate either immediately, or they develope into sporangia with swarmspores, having always two cilia. Only one oospore is formed in each oogonium; its contents (Fig. 89) divide into a centrally placed egg-cell and the “periplasm” surrounding it; this is of a paler colour and on the maturity of the oospore forms its thick, brown, external covering.

Fig. 88.—Polyphagus euglenæ. A with smooth, B with thorny oospores; m and f the two conjugating cells.

Fig. 89.—Peronospora alsinearum. Mycelium with egg-cell and antheridium.

Fig. 90.—Phytophthora infestans (strongly magnified). Cross section through a small portion of a Potato-leaf (the under side turned upwards): a the mycelium; b b two conidiophores projecting through a stoma; c conidia; e the spongy tissue of the leaf; g the epidermis.

The Potato-fungus (Phytophthora infestans) is of great interest. Its thallus winters in the Potato-tuber; other organs for passing the winter, such as oospores, are not known. When the tuber germinates, the Fungus-hyphæ penetrate the young shoot and keep pace with the aerial growth and development of the plant. The conidiophores emerge through the stomata, especially on the under side of the leaves; they branch like a tree (Fig. 90), and appear to the naked eye as a fine mould on the surface of the plant. The disease soon makes itself known by the brown colouring of those parts of the plant which are attacked, and by their withering. An ovoid conidium arises at first by the formation of a dividing wall at the apex of each branch of the conidiophore (Fig. 90 c c), and immediately underneath it another is formed, which pushes the first to one side, and so on. These conidia sometimes germinate directly, and form a mycelium, but most frequently their protoplasm divides into many small masses, each of which becomes a pear-shaped zoospore provided with two cilia (Fig. 91). Water is required for their germination, and when the ripe conidia are placed in a drop of water the swarm-cells are formed in the course of about five hours. They swarm about in rain and dewdrops in the Potato-fields, and are carried with the water to the Potato-plants and to the tubers in the soil. The wind also very easily conveys the conidia to healthy Potato-fields and infects them. The enormous quantity of conidia and swarm-cells that may be formed in the course of a summer explains the rapid spreading of the disease; and the preceding makes it clear why wet summers are favourable to its existence. When the swarm-cells germinate, they round off, and then surround themselves with a cell-wall which grows out into the germ-tube, and pierces through the epidermis of the host-plant (Fig. 92). Having entered the host, a new mycelium is formed. The potato disease, since 1845, has been rampant in Europe; it has, no doubt, been introduced from America, which, it must be remembered, is the home of the Potato-plant.

Fig. 91.—Phytophthora infestans: a-c conidia detached; in c the swarm-cells are leaving the mother-cell; d two free-swimming swarm-cells.

Fig. 92.—Phytophthora infestans. Cross section through a portion of a Potato-stalk. Two germinating conidia (a, b) piercing the epidermis, and the mycelium penetrating the cells.

The conidia exhibit various characters which are employed for the separation of the genera. Pythium is the most simple form. The contents of the terminally-formed conidia emerge as a spherical mass and divide into swarmspores. P. de Baryanum lives in the seedlings of many different Flowering-plants, which it completely destroys.—Phytophthora is distinguished by the circumstance that the sparsely-branched conidiophores bear, sympodially, chains of conidia. Besides the Potato-fungus (see above), Ph. fagi belongs to this group; it developes oospores very abundantly, and does great harm to seedlings of the Beech, Sycamore, and Pine trees.—Peronospora generally has conidiophores which are repeatedly forked, and bear a conidium on each of the most extreme ramifications. Many do great harm to their host-plants. P. viticola, on Vines, and P. nivea, on umbelliferous plants, have swarmspores, which are absent in the following species of this genus: P. sparsa, on Roses; P. gangliformis, on composites; P. alsinearum, on Stitchwort; P. parasitica, on cruciferous plants; P. viciæ, on Vetches and Peas; P. schachtii, on Beets; P. violacea, on the flowers of Scabiosa; P. radii, on the ray-florets of Matricaria.—Cystopus (Albugo) has the conidia developed in chains, which form a cohesive white layer underneath the epidermis of the host-plant. Cystopus candidus, on cruciferous plants, especially Shepherd’s Purse and Brassica; the germination commences on the cotyledons, and from this point the mycelium developes together with the host-plant; C. cubicus, on the leaves of Compositæ.

Fig. 93.—A fly overgrown with Saprolegnia.

Fig. 94.—Formation of swarmspores in a Saprolegnia: a germinating swarmspores.

Order 3. Saprolegniaceæ, Water-Fungi which live as saprophytes on organic remains lying in water, for instance, on dead flies (Fig. 93), worms, remains of plants; but they may also make their appearance on living animals, being frequently found, for example, on the young trout in rearing establishments.

Fig. 95.—Oogonium with two antheridia, Achlya racemosa.

The thallus is a single, long and branched cell. It has one portion which serves as root, and lives in the substratum, where it ramifies abundantly for the purpose of absorbing nourishment; and another portion projecting freely in the water, and sending out hyphæ on all sides (Fig. 93). The asexual reproduction takes place by swarmspores (Fig. 94), which are developed in large sporangia; these swarmspores generally possess two cilia, and on germination grow into new plants. The entire protoplasm in the oogonium is formed into one or more oospheres, without any surrounding “periplasm.” The oospheres may not be fertilised (p. 100), and then develope parthenogenetically.

Genera: Saprolegnia, whose swarmspores disperse immediately after having left the sporangium. S. ferax is the cause of a disease in fish (“Salmon disease”) and in the crayfish.—Achlya, whose swarmspores accumulate in a hollow ball before the mouth of the sporangium.—Leptomitus has strongly indented hyphæ, causing a “linked” appearance. L. lacteus is frequent in the waste matter from sugar factories.—Monoblepharis deviates from the others by the greater development of its fertilising process; the oosphere, situated in an open oogonium, becoming fertilised by self-motile spermatozoids, which are provided with a cilium at the posterior end.

Class 2. Mesomycetes.

The Mesomycetes are intermediate forms between the Phycomycetes and the Higher Fungi. In the vegetative organs, and in the multicellular hyphæ, they resemble the Higher Fungi; the methods of reproduction, however, show the characters of the Phycomycetes, namely sporangia and conidiophores of varying size and with varying number of spores; definite and typically formed asci and basidia are not present. Sexual reproduction is wanting. The Hemiasci are transitional between the Phycomycetes and the Ascomycetes, the Hemibasidii (Brand-Fungi) form the transition to the Basidiomycetes.

Sub-Class 1. Hemiasci.

The Hemiasci are Fungi with sporangia which, although resembling asci, yet have not, however, a definite form and a definite number of spores. Besides endospores, conidia, chlamydospores and oidia are found.

Order 1. Ascoideaceæ. Ascoidea rubescens forms irregular, reddish-brown masses in the sap issuing from felled Beeches. It has free sporangia, which resemble asci in their structure, in the development and ejection, and in the definite shape and size of the spores. The formation of the sporangia takes place when the nutriment is nearly exhausted, and resembles that of the conidia, since they are developed from the end of a hypha which enlarges, and the swelling becomes separated by a transverse wall. Within the sporangia numerous spores of a cap-like form are developed, which are set free through an opening at the apex. Sporangia are formed successively at the apex of the same hypha, the second commencing to develope as the first is dehiscing. Conidia and sporangia are not formed simultaneously; the former may be considered as closed sporangia.

Order 2. Protomycetaceæ. Protomyces pachydermus causes hard swellings on the stems and leaf-stalks of the Cichorieæ (Taraxacum, etc.). These swellings consist of chlamydospores (resting-spores), which germinate and become free, ascus-like sporangia, with numerous small spores. In nutritive solutions the chlamydospores form conidia with yeast-like buddings. P. macrosporus on Ægopodium, and other Umbelliferæ.

Order 3. Thelebolaceæ. Thelebolus stercoreus, is found on the dung of deer, hares, and rabbits, and has closed sporangia, which resemble asci in their shape and regular construction, and in the ejection of spores. The covering encloses only one sporangium, even where the sporangia arise close together.

This order, by reason of the covering of the sporangia, forms the transition from the Hemiasci to the Carpoasci, while the two first supply an intermediate step to the Exoasci.

Sub-Class 2. Hemibasidii, Brand-Fungi.

The Brand-Fungi (also known as Ustilagineæ) are Fungi with basidia-like conidiophores, which, however, have not yet advanced to a definite form or number of conidia. They are true parasites, whose mycelium spreads itself in the intercellular spaces of Flowering plants. The mycelium is colourless, quickly perishable, has transverse walls at some distance from each other (Fig. 96), and sends out haustoria into the cells of the host-plant.

Fig. 96.—Entyloma ranunculi. 1. Cross section of a portion of a leaf of Ficaria permeated by the mycelium; a bundle of hyphæ with conidia emerging from a stoma; in one of the cells are found four brand-spores. 2. A brand-spore developed in the middle of a hypha.

It most frequently happens that the germ-tube enters the host-plant at its most tender age, that is, during the germination of the seed; the mycelium then wanders about in the tissues of the shoot during its growth, until it reaches that part of the plant where the spores are to be formed. The spore-formation takes place in the same way in all those species whose brand-spores are developed in the floral parts of the host-plant. Many Brand-Fungi have, however, a more local occurrence, and the mycelium is restricted to a smaller area of the leaf or stem. Those organs of the host-plant in which the brand-spores are developed often become strongly hypertrophied. In perennial plants the mycelium winters very often in the rhizome.

Fig. 97.—Doassansia alismatis. 1. A fruit-body, formed by a covering of oblong hyphæ, which encloses a mass of brand-spores, and is embedded in the leaf-tissue of the host-plant; 20 times natural size. 2. A germinating brand-spore, 500 times natural size. 3. Three connected resting-spores, 400 times natural size. 4. Two conidia grown together, 600 times natural size.

The brand-spores are the winter resting-spores of the Brand-Fungi. They arise in the tissues of the host-plant, which is often destroyed, and become free through the rupture of the epidermis; they are thick-walled, generally brown or violet, and very often possess warts, spines, or reticulate markings. Fruit-bodies, that is enclosed organs of reproduction, are found in few genera (Sphacelotheca, Graphiola; Doassansia, Fig. 97). In Tolyposporium, Tuburcinia, Thecaphora (Fig. 102), etc., the brand-spores are united into a ball of spores. On germination the brand-spores behave as chlamydospores, namely, as the fundament of conidiophores, by emitting a short germ-tube, i.e. a conidiophore (“promycelium”). The Ustilaginaceæ (Fig. 99, 2) have a short transversely divided conidiophore, with laterally developed conidia (comp. the basidia of the Protobasidiomycetes). The conidiophores of the Tilletiaceæ are undivided (unicellular promycelia), and bear the conidia terminally, and so resemble the basidia of the Autobasidiomycetes.

Fig. 98.—Tuburcinia. 1. T. trientalis. Hyphæ, some of which bear conidia at the apex, forcing themselves out between the epidermal cells on the under side of the leaf; 320 times natural size. 2. T. trientalis. A ball of spores in which some of the individual brand-spores are about to germinate; 520 times natural size. 3. T. primulicola: various forms of conidia (500 times natural size).

In Tilletia, Entyloma, Neovossia, Tuburcinia, the brand-spores germinate and form basidia-like conidiophores with spindle-shaped conidia; their mycelium, on the other hand, produces later only single, sickle-shaped conidia, so that two kinds of conidia are found, as in a few Basidiomycetes. In some species, e.g. Ustilago hordei, the brand-spores only germinate vegetatively and form a mycelium. In nutritive solutions (solutions of dung, etc.) where they live as saprophytes, the brand-spores of many species emit germ-tubes, and on these, yeast-like conidia are produced by repeated budding, which grow into mycelia only when the nutritive solution is exhausted. These conidia have not the power of producing alcoholic fermentation. The very numerous conidia, which are found in the dung of herbivorous animals, are probably the yeast-conidia of Brand-Fungi. The brand-spores, which are eaten by animals with the grain and hay, pass into the dung and without doubt give rise to a very rich multiplication of yeast-conidia.

Fig. 99.—Ustilago. 1. Formation of brand-spores. 2. Germinating brand-spore of U. perennans. 3. Germinating brand-spore of U. cardui (after Brefeld). 4. U. filiformis. a A brand-spore with developed basidium; b another, with a conidium; c with two conidia; d with two conidia placed diametrically opposite to each other; e, detached conidia which are growing into hyphæ.

Fig. 100.—Tilletia tritici: a an ear of Wheat in which all the grains are attacked by Stinkbrand; b a blighted corn surrounded by the chaff; c a blighted corn grown together with a stamen; d the same cut across; e a brand-spore; f, g, h germinating brand-spores; i germinating conidia; j the mycelium; k-k brand-spore-forming mycelium-threads. (c-h magnified 400 times; i-k 300 times.)

The conidia (also called “sporidia”) of many species unite generally into an H-form (Figs. 97, 4; 100 h; 101, 4). This union in pairs does not, however, take place with a view to germination, there is no fusion of nuclei, and therefore in this “fusion” there is no sexual act.

Order 1. Ustilaginaceæ. Conidiophores with transverse walls and lateral conidia.—Ustilago (Fig. 99) generally developes its spores in the floral organs of its host-plant, the ovary or anthers, where they arise from hyphæ, and form a slimy mass which when mature becomes a black dust.

To this order belong U. avenæ, parasitic on Oats, U. hordei and U. nuda (U. jenseni), on Barley; these are the usual cause of “Smut” on cereals. U. hypodytes on straw of Elymus and Agropyrum. U. filiformis in the leaves of Glyceria. U. caricis transforms the fruits of various species of Carex into black, dusty balls. U. violacea developes its violet spore-powder in the anthers of the Caryophyllaceæ. U. tragopogonis, transforms entire inflorescences of Tragopogon into a black-violet mass. Among the largest are U. grandis, which causes the large swollen nodes in the stem of Phragmites, and the Maize Blight, U. maydis, which produces outgrowths about the size of a hand on the spadix of the Maize.

Order 2. Tilletiaceæ. Conidiophores undivided, generally several conidia arise at their apices.—Tilletia tritici, the Stinkbrand on Wheat (Fig. 100). The mycelium lives in Wheat-plants, producing its spores in the ovary after the whole interior of this body has been destroyed by the mycelium, with the exception of the external layer of the wall of the ovary, which remains essentially unaltered and encloses the closely packed, firm mass of spores (Fig. 100 d). The grains of Wheat thus attacked are shorter and thicker than the sound ones, and the ears show the presence of this Fungus by their erect position, and the wide separation of the chaff (Fig. 100 a). The unpleasant odour of the ovary prior to the ripening of the spores, has given the name “Stinkbrand,” and, in like manner, its hardness when it encloses the ripe spores, is the reason of its being also called “Stonebrand.” On account of this hardness, the diseased grains are readily harvested together with the healthy ones, which become infected by the spores at the threshing. T. lævis (T. fœtens) also occurs on Wheat and has smooth brand-spores.

Fig. 101.—Urocystis. 1, U. covalloides. A spore-ball, magnified 450 times. 2–4, U. anemones: 2–3, brand-spores which are about to germinate (magnified 450 times). 4, Conidia, the two in a state of fusion, a third with vacuoles and division-wall, magnified 500 times.

Entyloma (Fig. 96), a genus with numerous species, which appear in spots on the leaves of the host-plant, and Tuburcinia (Fig. 98), which makes its appearance on the Primulaceæ, produce white conidia-spots on the surface of the host-plant. The first-named has single spores, the latter has its spores closely massed together.—Urocystis (Fig. 101) has its spores surrounded by a number of small and lighter coloured barren spores. U. occulta, Rye-stem Blight, forms its spores in long streaks in the stems and leaves of the Rye, and does considerable damage. U. cepulæ on Onions. U. violæ forms large dark-violet swellings in the leaf-stalk and stems of Violets.—Thecaphora (Fig. 102) appears in seedlings of Convolvulus and Astragalus.

As a means of protection against the Smut-Fungi which make their appearance on the different cereals, a submersion of the grains in a solution of blue vitriol (½%) for twelve hours, or better still, submerging for five minutes in water heated to 53–55° C (Jensen’s method) is employed.

Fig. 102.—Thecaphora. 1, T. convolvuli, a ball of spores, one of the brand-spores has emitted a septate branched conidiophore (× 520). 2, T. affinis, a ball of spores (× 520).

Class 3. Mycomycetes, Higher Fungi.

The Mycomycetes are not entirely aquatic in habit; they have hyphæ with transverse walls, but no sexual reproductive organs. The asexual reproduction takes place in very different ways; by endospores (in asci), conidia, basidiospores, chlamydospores, and oidia. Swarmspores are never found.

Two chief methods of reproduction may be distinguished, and hence the class may be divided into two large sub-classes:—the Ascomycetes (with asci), and the Basidiomycetes (with basidia).

Sub-Class 1. Ascomycetes.

The main characteristic which distinguishes the Ascomycetes is the ascus; a name given to a sporangium of a definite shape and size, and containing a definite number of spores. The shape is generally club-like or spherical, the number of spores 8 (in some 2, 4, 16 or more), see Figs. 103, 105, 108, 110, 113, 116, 120, 121, 123, 129.

In the lowest forms, the Exoasci, the ascus springs directly from the mycelium without the formation of a fruit-body (i.e. ascocarp). In the higher forms, which contain many species, the Carpoasci, the asci are united and form ascocarps which may be more or less enclosed (angiocarpic, hemiangiocarpic, and probably gymnocarpic).

Fig. 103.—Endogenous formation of spores in Peziza confluens. In the youngest asci there is only one nucleus (b, e); this divides into two (f); and the division is repeated so that there are 4 nuclei in c and 8 in g. These surround themselves with protoplasm and a cell-wall (h, i). The protoplasm of the mother-cell is not entirely used up.

The hyphæ of the Mycelium in some remain free, in others they are felted together and form thick strands or flat, cushion-like bodies (compare in particular the stromata of the Pyrenomycetes). Some species form sclerotia (Figs. 116, 128).

Asexual reproduction by means of conidia is known in many species as the principal means of reproduction, and the one which affords the most rapid means of distribution. The conidia may be produced on conidiophores (Fig. 109), in conidial-layers (Fig. 122), and often in conidiocarps (pycnidia, Figs. 120 d, e; 123 a; 124 b.). These last occur partly as the so-called “spermogonia” (that is, pycnidia with microconidia). The conidiophores never approach the basidia.

In many species the ascospores germinate and form conidia immediately (Nectria cinnabarina, Sclerotinia, Taphrina, etc.), sometimes while they are still in the ascus and before their ejection (Taphrina, Fig. 105 a). In many instances the conidia by means of continued budding can, for a longer or shorter time, produce yeast-conidia, e.g. Taphrina. In many other cases the conidia arise from the germ-tubes of the ascospores, or at any part of the mycelium. The unripe asci of Taphrina, when placed in water, develop conidia at their apices. The Sclerotinia-species produce numerous conidia whose germination has never been observed. The formation of conidia and asci sometimes takes place on the same fruit-body. In Heterosphæria patella the conidia and asci are developed successively in the same fruit-body; in the ascocarps of Dermatea frangula and Sclerotinia sclerotiorum the formation of conidia may take place. The ascocarps frequently arise from the conidial-layers (Nectria cinnabarina, etc.). This relationship of the two forms of reproduction to each other may be explained by considering that both have descended phylogenetically from sporangia.

Sometimes chlamydospores and oidia also appear in the Ascomycetes; on germination, however, they do not, as in Protomyces, form sporangia, and on this account cannot be distinctly distinguished from conidia.

The asci are morphologically the highest form of reproduction and are always found at the close of the development of these Fungi; the accessory forms of reproduction are first developed, but a well-defined alternation of generations does not occur.

In the Ascomycetes there are more than 11,000 described species, which can be classed as follows:—

Series 1. Exoasci. Only one order.

„ 2. Carpoasci.

Family 1. Gymnoascales, }

„ 2. Perisporiales, } Angiocarpic Carpoasci.

„ 3. Pyrenomycetes, }

„ 4. Hysteriales, }

„ 5. Discomycetes,} Hemiangiocarpic Carpoasci.

„ 6. Helvellales, Gymnocarpic (?) Carpoasci.

Additional Ascolichenes: Lichen-forming Ascomycetes.

Series 1. Exoasci.

Ascomycetes with FREE ASCI; sometimes also conidia, chlamydospores and oidia. One order.

Order. Taphrinaceæ. Of the genera belonging to this order, Taphrina, Endomyces, and Ascocorticium, the first is most important.

Endomyces decipiens is a parasite in the fruit-body of Armillaria mellea; E. magnusii lives in the gelatinous, fermenting exudations of Oak-trees; Ascocorticium albidum is found under the bark of the Fir-tree. Endomyces has chlamydospores and oidia.

The species of Taphrina are parasites, whose free asci may be found in great numbers, generally closely pressed together, on the parts of plants which they have attacked. The asci are developed directly from the ascogenous cells of a fertile, generally sub-cuticular, hypha, which arises from the sterile mycelium. The latter arises from the germinating ascospore, and may hibernate in the tissues of its host, particularly in the winter buds, and then with the commencement of the next period of vegetation it continues its growth side by side with that of its host. The hyphæ ramify in the intercellular spaces or beneath the cuticle, but have no haustoria. The ascospores (Fig. 105 A) and unripe asci may produce conidia.

Fig. 104.—Taphrina (Exoascus) pruni. Yeast-like budding of a germinating spore (× 600).

Fig. 105.—Taphrina betulina: a ascus filled with conidia; b germinating spores (× 600).

Very remarkable appearances, and swellings of the attacked tissues, are produced when the mycelium is perennial; for example, the “Witches’-brooms” and “Pockets.” The hard, hollow, stoneless plums, known as “Pocket” or “Bladder” Plums, are produced by considerable changes in the tissues of the fruit; these are caused particularly by T. pruni on several species of Prunus. The “Witches’-brooms,” on the contrary, are deformations of entire twigs or branches, and often attain a very large size. They occur on Alnus incana, caused by T. epiphylla; on Carpinus betulus, by T. carpini; on Cherry-trees, by T. cerasi; on Plum-trees, by T. insititiæ; on Birches, by T. turgida and T. betulina. T. deformans attacks the leaves of the Peach, and causes them to curl.

When a perennial mycelium is wanting, the infection is confined as a rule to white or yellow spots on the leaves, e.g. the commonest, T. sadebeckii, on Alnus glutinosa, and T. aurea on species of Populus. T. alni incanæ (Fig. 106) causes considerable hypertrophies on the pistillate catkins of the Alder, which may be compared to the “pockets” of Prunus.

Fig. 106.—Taphrina alni incanæ on the Alder (nat. size).

Series 2. Carpoasci.

The Carpoasci are Ascomycetes, whose asci are enclosed in fruit-bodies, i.e. ascocarps. The accessory means of reproduction are free conidiophores (Fig. 109), conidial-layers (Fig. 122), conidiocarps (Fig. 120 D, E, etc.), chlamydospores and oidia.

For the different methods of distributing the ascospores, see p. 92.

Of the six families of the Carpoasci, the first three—Gymnoascales, Perisporiales, and Pyrenomycetes—are ANGIOCARPIC (that is, the ascocarp remains closed throughout its existence, and does not dehisce when ripe); the fourth and fifth families (Hysteriales and Discomycetes), on the other hand, are HEMIANGIOCARPIC (the ascocarp, here also called an apothecium, is closed in the early stages, but opens at the commencement of ripening and exposes a hymenium of crowded asci); the family of Helvellales has probably GYMNOCARPIC (or hemiangiocarpic) fruit-bodies.

Family 1. Gymnoascales.

The ascocarps are surrounded by a spongy and incomplete envelope. One order, poor in species.

Order Gymnoascaceæ.—The ascocarps are borne sometimes solitarily, or sometimes coiled together. Gymnoascus reessii forms small bodies about 1 mm. in diameter on old horse-dung, which at first are white and afterwards orange-red.—Ctenomyces serratus lives on the old feathers in birds’ nests.

Family 2. Perisporiales.

The ascocarps are surrounded by a complete envelope without any opening: the fruit-bodies are cleistocarpic; the spores are only liberated after the disintegration of the fruit-bodies. Paraphyses are wanting. The two first orders have in addition the means of reproduction by conidia.

Order 1. Erysiphaceæ, Mildews. The Fungi belonging to this order are epiphytic parasites, whose mycelium, somewhat resembling a cobweb, may be seen on the leaves and other green portions of plants (see Figs. 107, 108). The hyphæ ramify in all directions upon the surface of their host, and emit haustoria which penetrate the epidermal cells, and thus derive the necessary nutriment. The Mildew-Fungi thus belong to the obligate parasites, and during their growth dwarf and destroy the portions of their host on which they live. The reproduction takes place in the first instance by abstriction of conidio-chains from the end of special branches (Fig. 108 c, a hypha is seen in the act of detaching a conidium). The conidia may germinate immediately, and thus quickly reproduce their species. When present in large numbers they appear as a white meal covering the surface of the plant on which the fungus is found. Later on appear the dark brown, spheroid ascocarps (Fig. 108 a) which, although small, are generally just visible to the naked eye as black specks.

Fig. 107.—Erysiphe cichoracearum: a mycelium-threads; b sterile hypha (“pollinodium”); c fertile hypha (ascogone or archicarp); d and e young ascocarps.

A characteristic feature of the Mildew-Fungi is the thin, pseudo-parenchymatous covering of the ascocarp, enclosing one (Podosphæra and Sphærotheca; compare Thelebolus among the Hemiasci) or a few asci (Fig. 108 c), which do not form any hymenium, but are irregularly placed. The cells of the ascocarp-envelope are often prolonged into hair-like appendages. The ascocarps are developed from the mycelium at places where two hyphæ cross each other (Fig. 107). At these places two short and erect hyphæ are produced side by side. The one from the lower hypha (Fig. 107 c) assumes an ellipsoidal shape, and is known as the archicarp or ascogone, while the other (“pollinodium”) arches over the ascogone. From the latter one ascus may be at once developed (Sphærotheca, etc.), or after its division several asci may be produced, each developed from one division. The sterile hypha (termed “pollinodium,” since it was formerly, but erroneously, supposed to fertilise the ascogone) produces a number of branches, and forms the pseudo-parenchymatous envelope of one cell in thickness, enclosing the asci.

Fig. 108.—Erysiphe communis. A small portion of a leaf with this Fungus growing upon it (considerably magnified). The hyphæ b and d do not belong to this Fungus, but are reproductive organs of a pyrenomycetous Fungus parasitic upon it (Cicinnobolus).

Many plants, both cultivated and wild, are attacked by various species of Mildew. A common means of prevention against their attacks is to dust the diseased parts with sulphur.

Fig. 109.—Eurotium glaucum: α portion of mycelium lying horizontally; β vertically-placed conidiophore; the mycelium gives rise to another branch near α; the conidia are abstricted from short flask-shaped cells; b a ripe conidium; c, d germinating conidia; e spirally-twisted hypha, commencement of an ascocarp; f a stage later; g still later, the hypha at the base of the coil has given off branches which are applied to it; h, i sections of young ascocarps.

Sphærotheca pannosa occurs on the leaves of Roses, and on the fruit of Peaches and Apricots. S. castagnei on Humulus, Cucumis, etc.—Erysiphe tuckeri grows on the leaves and fruit of the Vine; it spins its hyphæ over the bunches of grapes, curtails their growth, and causes them to burst, and to become decayed and rotten (Grape-disease). The Fungus was first noticed in England in 1845, and later was found in all countries where grapes are grown. It is only known in the conidial form (“Oidium tuckeri”). Many other species of Erysiphe are found on herbaceous plants.—Microsphæra has appendages which are repeatedly forked at their extremities. M. grossulariæ on Ribes grossularia.—Uncinula has appendages with spirally-coiled extremities; on Salix and Acer.—Phyllactinia has a circle of bristle-like appendages with dilated bases. P. guttata on Corylus, Fraxinus, Fagus, etc.

Order 2. Perisporiaceæ, Moulds and Mildews. A group of Fungi widely distributed and found in all situations. Usually they have a well-developed surface mycelium, and small, round, seldom conspicuous ascocarps, containing ovoid, pulley-like spores. They are partly saprophytic, partly parasitic, in the latter condition having a brown mycelium.

Fig. 110.—Eurotium glaucum: a longitudinal section of a half-ripe ascocarp, bounded externally by a well-defined layer of cells, enclosing asci in various stages of development; b a semi-ripe, c an almost ripe ascus; d and e spores seen from the edge and side; f germinating spore twenty-two hours after been sown in plum juice.

Eurotium glaucum (= E. herbariorum, Figs. 109, 110) and E. repens live on dead organic matter, preserved fruits, etc. The conidial forms of both species are known as “Moulds” (Fig. 109), and formerly were described under the name “Aspergillus glaucus.” The conidia for some time remain attached to each other in chains (Fig. 109 a); they are abstricted from sterigmata arranged radially on the spherical, swollen end of the conidiophore. The small yellow or brownish ascocarps are frequently found in herbaria, especially when the specimens have been insufficiently dried. Aspergillus fumigatus and others are pathogenic, causing mycosis in warm-blooded animals.

Fig. 111.—Penicillium crustaceum: a conidia (× 300); b germination of conidia; c small portion of mycelium, produced from a conidium at *, with five conidiophores; d young conidiophore (× 630), a flask-shaped cell is abstricting a conidium; e the same conidiophore after 9–10 hours.

Fig. 112.—Penicillium crustaceum: a two spirally-coiled hyphæ arise from the mycelium, from one of which (archicarp) the asci are produced; b a further step in the development of the ascocarp; the branching archicarp is surrounded by sterile hyphæ; c section of young ascocarp; the larger hyphæ in the centre are the ascogenous hyphæ; these are enclosed by a pseudo-parenchyma of sterile hyphæ (× 300); d series of ripe asci with spores; e four ascopores seen laterally; f germinating ascospores (× 800).

Penicillium crustaceum (P. glaucum, Figs. 111, 112) is an exceedingly common “Mould.” Its mycelium appears very frequently on any organic matter which is permitted to remain untouched, and soon covers it with a dense mass of blue-green conidiophores. These branch at their summits and bear flask-shaped cells from which the conidia are abstricted. The ascocarps which, both in size and colour, resemble grains of sand, have only been obtained in luxuriant cultivation with a limited supply of oxygen.

Capnodium salicinum (Fumago salicina, Cladosporium fumago), a common Mildew, forms dark overgrowths on the leaves and branches of various shrubs (Poplars, Elms, Willows) and on Hops. The conidia appear in various forms, as on conidiophores, in conidiocarps with large multicellular conidia, and in conidiocarps with small unicellular conidia; in nutritive solutions yeast-like conidia are also developed.—Apiosporium pinophilum produces mildew on the leaves of Abies alba and Picea excelsa. (The conidial-forms were formerly described as “Antennaria pinophila”).

Order 3. Tuberaceæ, Truffles. The Fungi belonging to this order are entirely subterranean. The mycelium is filamentous, and partly parasitic upon the roots of plants, especially trees, in its neighbourhood; it is then known as Mycorhiza. The fruit-body is relatively large, in some cases about the size of a hen’s egg. Internally it is traversed by a number of winding passages (Fig. 113 a), the walls of which are coated with the asci. The asci (b) contain only a small number of spores, and these are set free by the putrefaction of the fruit-body. Conidia are unknown.

Fig. 113.—Tuber melanosporum: a fruit-body (nat. size), a portion having been removed to show the internal structure; b an ascus with ascospores.

Tuber melanosporum, T. brumale, T. æstivum, and other species are edible. Terfezia leonis and Choiromyces mæandriformis are also edible. The Truffles are always found in woods and under trees, and disappear when these are destroyed. France and Italy produce the best and the largest number of Truffles, which are hunted by specially trained dogs and pigs.

In Elaphomyces (Stag-Truffle) the fruit-body has a corky external layer, and is inedible. Some of the species are found in this country. E. granulatus is parasitic on the roots of the Fir.

Family 3. Pyrenomycetes.

In this family the hymenium is enclosed in small fruit-bodies, perithecia (Fig. 120 b), which appear to the naked eye as small dots. In shape they resemble a globe or a flask with a narrow mouth, through which the spores are ejected (peronocarpic ascocarps). Different kinds of reproduction—conidia, pycnidia (chiefly with microconidia), chlamydospores, and perithecia—are found in the same species. The various stages in the life-history of these Fungi are so dissimilar, that formally they were considered to be different genera. Ergot furnishes a very good example.

Fig. 114.—A small portion of an ovary attacked with Claviceps purpurea (Sphacelia).

Fig. 115.—An ovary with the conidial stage of Claviceps purpurea (Sphacelia).

This family may be subdivided into 3 sub-families.

Sub-Family 1. Hypocreales.

The perithecia are pale, fleshy, brightly coloured, and generally aggregated on a stroma. Conidia and chlamydospores occur very frequently. Only one order.

Order. Hypocreaceæ. In this order the majority are parasites upon Flowering-plants (Nectria, Polystigma, Epichloë, Claviceps); but some are parasites upon Fungi (Hypomyces, Melanospora), or upon insects (Cordyceps).

Fig. 116.—Claviceps purpurea. A Sclerotium with stromata (cl) (× by 2). B Stroma divided longitudinally to show the perithecia (cp). C A perithecium with the surrounding hyphæ (hy). D An ascus ruptured, with the eight filamentous ascospores emerging.

The most important member of this order is the Ergot (Claviceps purpurea, Figs. 114, 115, 116). This Fungus is found in the flowers of many species of Grasses, especially the Rye, attacking and destroying the ovaries. In the FIRST or CONIDIAL STAGE of the attack, the ovaries are found covered with a white, irregularly folded mycelium (Fig. 114 m, Fig. 115), formed of numerous hyphæ woven together and penetrating the wall of the ovary. From these a number of hyphæ (Fig. 114 a) project into the air and abstrict from their apices the conidia (b) which serve as reproductive organs. The mycelium also secretes a sticky, stinking fluid (honey-dew) in which the conidia are embedded in great numbers. The honey-dew exudes from the bases of the glumes, and is greedily sought by flies, which thus carry the conidia to other ovaries. In this manner fresh ears are infected, which might escape were the conidia only distributed by the wind. This stage formerly was regarded as an independent Fungus, known as Sphacelia segetum (Fig. 115). On germination, the conidia produce either a new mycelium (Fig. 114 d, c), or new conidia. The SECOND or SCLEROTIUM STAGE is the one in which the Fungus passes the winter. The mycelium penetrates deeper and deeper into the attacked ovaries, their tissues are destroyed and replaced by the hyphæ, which gradually become more and more felted together. A firm, pseudo-parenchymatous mass of hyphæ is thus formed at the base of the loosely-woven Sphacelia, which is in part transformed into the hard sclerotium, and the remainder thrown off. A dark, hard, poisonous body, longer than the natural grain, is thus formed; these bodies are known as Ergots, and were formerly considered to be a distinct species,—Sclerotium clavus (“Secale cornutum,” Ergot, Fig. 116 A, c). The THIRD STAGE, described as Claviceps purpurea, is developed in the following spring from the germinating sclerotium, which produces dark-red stromata with short stalks. In the stroma numerous perithecia with asci and ascospores are produced. The latter may infect young flowers of the cereals, in which the disease is then developed as before.

Fig. 117.—Nectria cinnabarina: a branch of Acer pseudoplatanus, with conidial-layers and perithecia (nat. size); b a conidial-layer (Tuberculoria vulgaris); c, a mass of perithecia. (b and c × 8.)

Several species of the genus Nectria, with blood-red perithecia, are found as dangerous parasites, especially N. ditissima, which causes “Canker” in the Beech, Ash, and Apple, etc.; N. cucurbitula, which appears on Pine-trees, and N. cinnabarina (Fig. 117), whose conidial form was formerly named Tubercularia vulgaris.—Polystigma rubrum forms shining red spots on the green leaves of Prunus-species.—Epichloë typhina is parasitic on the sheaths of Grasses, on which it first forms a white conidial-layer, later on a yellow layer of perithecia.—Cordyceps (Chrysalis Fungus, Figs. 118, 119) lives in and destroys insects, and after compassing their death produces the club-formed, generally yellow, stromata, one part of which bears conidia (Isaria) and another perithecia. C. militaris (Fig. 118) on the chrysalides and caterpillars of moths, is the most common.

The so-called Botrytis bassiana, which produces the disease known by the name of “Muscardine,” in silkworms, is probably a conidial form belonging to Cordyceps.

Fig. 118.—Cordyceps militaris. I Stromata with conidiophores (Isaria farinosa). II A larva, with stromata, bearing perithecia. III A spore.

Fig. 119.—Cordyceps robertii on the larva of Hepialus virescens: a stalk of stroma; b perithecia.

Sub-Family 2. Sphæriales.

To this sub-family belong the majority of the Pyrenomycetes. The perithecia are of a firm consistence (tough, leathery, woody or carbonaceous), and of a dark colour. Their covering is quite distinct from the stroma when this structure is present. The stromata are sometimes very large, and may be either cushion-like, crustaceous, upright and club-like, or branched bodies. In general, small, inconspicuous Fungi, living on dead vegetable matter, sometimes parasites. Free conidiophores and conidiocarps are known in many species, and in several, chlamydospore-like forms of reproduction. Orders 3–18 constitute the Sphæriaceæ of older systematists.

Fig. 120.—Strickeria obducens: a a portion of an Ash-branch with the bark partly thrown off; on the wood are numerous black perithecia (× 20); b longitudinal section through a perithecium; c a spore; d longitudinal section through a pycnidium whose ascospores are being ejected; e portion of the same, with hyphæ and spores.

Order 1. Sordariaceæ.—Fungi living on dung with fragile perithecia, either aerial or buried in the substratum. The dark brown or black spores have either a mucilaginous envelope (Sordaria, etc.) or mucilaginous appendages (Podospora), by means of which their expulsion and distribution are promoted.

Order 2. Chætomiaceæ. Perithecia fragile, free, bearing on the summit a tuft of hairs. Chætomium, on decaying vegetable matter.

Orders 3–7. Perithecia scattered or aggregated, situated from the commencement on the surface of the substratum. Stroma wanting.

Order 3. Trichosphæriaceæ. Trichosphæria parasitica (Fig. 121), on Abies alba; Herpotrichia nigra on Picea excelsa and Pinus montana.

Fig. 121.—Trichosphæria parasitica: a a twig of Abies alba, with epiphytic mycelium; b a leaf with mycelium and sporangia (magnified); c a sporangium (× 60); d an ascus with spores (× 550).

Order 4. Melanommaceæ. Rosellinia quercina lives in the roots of 1–3-year-old Oaks, and destroys the plants.

Order 5. Ceratostomaceæ.

Order 6. Amphisphæriaceæ. Strickeria obducens (Fig. 120) has brick-like spores, and lives aggregated on the hard branches of Fraxinus.

Order 7. Lophiostomaceæ.

Order 8. Cucurbitariaceæ. Perithecia tufted, at first embedded, then breaking through, often situated upon an indistinct stroma.

Orders 9–13. The perithecia remain embedded, and are only liberated by the casting off of the covering layers of the substratum. Stroma wanting.

Order 9. Sphærellaceæ. The species of Sphærella have colourless, bicellular spores. They live upon the leaves of many plants, and develope spherical perithecia upon the fallen leaves.

Order 10. Pleosporaceæ. The conidial-forms of Pleospora herbarum and P. vulgaris form a black covering on various plants, known as “smuts.”—Venturia ditricha occurs on the underside of dry Birch leaves, and perhaps to this belongs the conidial-form, Fusicladium pirinum, which causes the “Rust spots” on Apples and Pears.

Order 11. Massariaceæ.

Order 12. Clypeosphæriaceæ.

Order 13. Gnomoniaceæ. Perithecia, with peak-like aperture. Gnomonia erythrostoma in the leaves of Prunus avium, which turn brown and do not fall in autumn.

Orders 14–18. Stroma generally well developed. The perithecia are embedded in the stroma, but when this is rudimentary, in the substratum.

Order 14. Valsaceæ. Valsa.

Order 15. Diatrypaceæ. Diatrype.

Order 16. Melanconidaceæ.

Order 17. Melogrammataceæ.

Order 18. Xylariaceæ. This order is the most highly developed of the Sphæriales. The stroma arises on the surface of the substratum, which is generally dead or decorticated wood; it is well-developed, crustaceous, hemispherical or upright. In the younger conditions it is covered with a layer of conidia, and later on it bears the perithecia, arranged in a layer immediately beneath its surface. The ascospores are of a dark colour. Often also there are free conidiophores.

Fig. 122.—Xylaria hypoxylon (nat. size) on a tree stump: a younger, b an older stroma, both of which, with the exception of the black lower portion, are covered with white conidia; n, spot where the perithecia are developed; c an old stroma with upper part fallen off; d, e large branched stromata; k conidia.

Hypoxylon and Ustulina have a cushion-like or crustaceous stroma.—Xylaria has a club-shaped or branched stroma, often several centimetres high. X. hypoxylon (Fig. 122) and X. polymorpha occur on old tree stumps.—Poronia grows on old horse dung, and has a conical stroma.

Sub-Family 3. Dothideales.

The perithecia are always embedded in a black stroma, and are not distinctly separated from it. The accessory forms of reproduction are: conidiophores, conidiocarps, and yeast-like conidia. The majority are parasites. One order.

Order Dothideaceæ. Phyllachora graminis produces scab-like patches on the leaves of the Grasses.—Scirrhia rimosa grows on the leaf-sheathes of Phragmites.—Rhopographus pteridis on Pteridium aquilinum.

Family 4. Hysteriales.

This family, like the following, has hemiangiocarpic ascocarps (apothecia). These are closed in the early stages, but when ripe open in a valvular manner by a longitudinal fissure; they are black, oblong, and often twisted. Some species are parasites, especially upon the Coniferæ.

Fig. 123.—Lophodermium (Hypoderma) nervisequium: a two leaves of Abies alba seen from above with pycnidia; b a leaf seen from the underside with apothecia; c an ascus with ascospores. (× 500.)

Fig. 124.—Three leaves of the Red-pine with Lophodermium macrosporum: a under side of the leaves with apothecia; b a leaf from upper side with pycnidia. (× about 2.)

Fig. 125.—Lophodermium pinastri: a leaves of Pinus sylvestris with apothecia (nat. size); b two paraphyses and an ascus with filamentous spores.

Order 1. Hysteriaceæ. Hysterium pulicare upon the ruptured bark of many trees.

Order 2. Hypodermaceæ. The species of Lophodermium live upon the leaves of Conifers, and are the cause of their falling off (blight). L. pinastri (Fig. 125), on the leaves of Pinus and Picea; the leaves become red-brown and fall off; at first conidiocarps are formed, and later apothecia; L. nervisequium (Fig. 123), on Abies alba; L. macrosporum (Fig. 124), on Picea excelsa; L. brachysporum, on Pinus strobus.

Order 3. Dichænaceæ.

Order 4. Acrospermaceæ.

Family 5. Discomycetes.

The ascocarps (apothecia) are at first closed, and only open at the time of their ripening, not valvularly, but more or less like a saucer or cup, so that the hymenium lies exposed on their upper surface. In the first three sub-families, and generally also in the fourth, the apothecia are formed inside the substratum. The apothecia are, in contrast to the Pyrenomycetes, light and brightly coloured, and their size varies very much, and may be several centimetres in diameter. Paraphyses are often present between the asci; they often contain colouring matter, and give to the disc its characteristic colour. The tissue on which the asci are borne is known as the hypothecium. The shape and colour of the spores is not so varied as in the Pyrenomycetes. The accessory forms of reproduction are conidia (sometimes of two forms), chlamydospores, and oidia. The family is divided into 5 sub-families.

Sub-Family 1. Phacidiales.

The apothecia are developed in the interior of the substratum, which they break through, and in general dehisce apically. The envelope is tough and black. Hypothecium inconspicuous; hymenium flat.

Order 1. Euphacidiaceæ. Phacidium abietinum, on the leaves of Abies alba.—Rhytisma; the pycnidia are found in the summer on the green leaves, while the apothecia are developed on the fallen leaves and dehisce in the following spring. R. acerinum causes black spots on the leaves of the Sycamore, and R. salicinum on Willows.

Order 2. Pseudophacidiaceæ.

Sub-Family 2. Stictidales.

The apothecia when ripe break through the substratum which forms a border round them. Hymenium generally saucer-shaped.

Order 1. Stictidaceæ. Stictis.

Order 2. Ostropaceæ. Ostropa.

Sub-Family 3. Tryblidiales.

The apothecia are embedded in the substratum in the early stages, and then are raised high above it. Hypothecium thick. Hymenium cup-shaped.

Order 1. Tryblidiaceæ. Tryblidium.

Order 2. Heterosphæriaceæ. Heterosphæria patella on the dead stalks of Umbellifers.

Sub-Family 4. Dermateales.

The apothecia in the early stages are embedded in the substratum and then break through it, or are from the first situated on the surface of the substratum. Hypothecium thick.

Order 1. Cenangiaceæ. Cenangium.

Order 2. Dermateaceæ. Dermatea.

Order 3. Patellariaceæ. Patellea, Biatorella, Patellaria.

Order 4. Caliciaceæ. Calicium, Coniocybe, etc., on the bark of trees.

Order 5. Arthoniaceæ. Arthonia on the bark of several trees. Celidium stictarum on the apothecia of Sticta pulmonaria.

Order 6. Bulgariaceæ. Apothecia gelatinous under moist conditions, and horny when dried.—Calloria fusarioides; the red apothecia break out in the spring on the dried stalks of Urtica dioica; a gelatinous reproductive form of the Fungus is found before the apothecia, which consists of oidia (formerly described as “Dacryomyces urticæ”).—Bulgaria inquinans on the living or fallen trucks of Oaks and Beeches.

Fig. 126.—Botrytis cinerea: a slightly magnified; b more highly magnified; c germinating conidium.

Fig. 127.—Sclerotinia fuckeliania: a sclerotium with conidiophores; b with apothecia; c section through sclerotium and apothecium; d ascus with eight ascospores. (× 390.)

Sub-Family 5. Pezizales.

The apothecia are developed on the surface of the substratum and are waxy or fleshy; at the commencement closed, and covered with a saucer- or cup-shaped, seldom flat, hymenium. The hypothecium is generally well developed. This sub-family is the richest in species of the Discomycetes and contains forms of very different habit. They grow upon dead wood, upon the ground, and upon dung. A few are parasites.

Order 1. Helotiaceæ. Apothecia with waxy envelope of colourless, or yellowish prosenchymatous cells.—Chlorosplenium æruginosum is found on decaying wood (particularly Oak and Birch), to which it gives a green colour. Sclerotinia has sclerotia which are developed upon the host-plant and from which, after a period of rest, the long, brown-stalked apothecia arise. S. ciborioides (S. trifoliorum, Fig. 128) is parasitic on Clover; S. sclerotiorum, on Daucus-roots, Phaseolus, etc.; S. baccarum, on the berries of Vaccinium myrtillus; “Botrytis cinerea” is a common parasite and is probably the conidial form of S. fuckeliania (Fig. 127).—Helotium herbarum lives on dry plant stems.—Dasyscypha willkommii (Fig. 129) produces Larch-canker on the bark of the Larch.

Fig. 128.—Sclerotinia ciborioides: a sclerotium with three apothecia slightly magnified; b ascus with eight ascospores; c germinating ascospore.

Fig. 129.—Dasyscypha willkommii: a portion of bark of Larix decidua with sessile, cup-shaped apothecia (nat. size); b two paraphyses on either side of an ascus with eight ascospores.

Order 2. Mollisiaceæ. Mollisia cinerea, principally on decaying wood.

Order 3. Pezizaceæ. This order contains the largest and morphologically the highest forms of the Discomycetes. Apothecia fleshy, and in the later conditions generally saucer-shaped.

Peziza, with sessile apothecia, growing on the ground; P. cochleata is brown, and coiled like a snail-shell; P. coccinea is scarlet; P. aurantia occurs as an orange-coloured expansion on the ground.

Order 4. Ascobolaceæ. Apothecia fleshy; in the later stages flat or convex. The asci are, comparatively speaking, large, and often contain a great number of spores which escape by the casting off of a lid on the summit of the ascus. Generally living on dung.—Ascobolus furfuraceus, etc.

Family 6. Helvellales.

These Fungi have the appearance of clubs, bells, or mushrooms, consisting of an upright stalk bearing a large and fleshy head, on the exterior surface of which the hymenium is spread. The ascocarps are probably gymnocarpic from the beginning, and on this account these plants are placed in a separate family. The development of the ascocarps is unknown. The Morchella (Morell) grows on the ground; some species are edible. 1 order.

Order. Helvellaceæ. Spathulea is yellow and club-shaped, and forms “fairy rings” in woods.—Geoglossum (Earth-tongue) projects above the ground as a black tongue, or as a club-shaped body. Several species are found in meadows and on heaths.—Helvella has a stalk, bearing an irregularly folded head, on the external surface of which is the hypothecium.—Morchella (Morell, Fig. 130), the stalk bears on its summit the conical or spherical head, the external surface of which is reticulate and bears the asci.—Mitrula. Verpa.

Fig. 130.—Morchella esculenta: a an entire specimen, about one half natural size; b longitudinal section through the head.

Appendix to the Ascomycetes:

Family 7. Ascolichenes (Lichen-forming Ascomycetes).

The Lichens were formerly classed among the Thallophyta as a group quite distinct from the Algæ and Fungi. Investigations during the last twenty-five years, however, have conclusively proved that the Lichens are Fungi which reproduce in the same manner as the Ascomycetes, or, more rarely, the Basidiomycetes, and have entered into a peculiar symbiotic relation with Algæ, especially the Cyanophyceæ and Protococcoideæ, with which they associate, and without which they would be unable to exist. The Fungus forms the largest portion of the Lichen, enclosing the Alga with which it may be said to be commensal. The Fungus especially produces reproductive bodies and absorbs the inorganic nourishment through the rhizoids, whilst the Alga supplies it with the organic materials. In consequence of this the Lichens, in contradistinction to other Fungi, need light for the development of their nutritive organs, and are therefore, in any case internally, of a more or less greenish colour. The form and condition of the thallus is unusual among the Fungi, and they can grow upon rocks and in other places where no dead organic matter, such as would be required by other Fungi, is obtainable.

Fig. 131.—Transverse section through the thallus of Sticta fuliginosa (× 500): r-r rhizoid-strands, which arise from the under side; g-g gonidial layer; m medullary layer; o upper, u lower cortex.

Two cellular forms are therefore to be found in each Lichen:

1. The cells which belong to the Fungus. These are generally septate, branched hyphæ without any trace of chlorophyll. In the thallus of the majority of Lichens there may be found a medullary layer (Fig. 131 m) of loosely-woven hyphæ, between which there are large air chambers; and an external layer (cortex) (Fig. 131 o, u) formed of closely-woven hyphæ without any intercellular spaces. In some Lichens (Collemaceæ) the hyphæ wind about in the thallus, being equally distributed throughout, without forming any decided strata. These Lichens moreover become gelatinous when exposed to moisture (Fig. 132), on account of the swelling of the walls of the Algæ. The hyphæ contain protoplasm with drops of oil, but never starch; their walls easily swell when exposed to damp after having been dried, and in some (e.g. Cetraria islandica) they become gelatinous when cooked. Certain strata of hyphæ become blue on treatment with iodine alone, from which it is inferred that the wall is allied, in its chemical nature, to starch.

2. The enclosed Algæ, termed “gonidia.” Some belonging to the Cyanophyceæ, Protococcoideæ, (especially Pleurococcus) and Chroococcaceæ, are spherical and are found isolated, or in irregular groups of cells (Fig. 131 g); some belonging to Nostoc (Fig. 132 g), Lyngbyaceæ, etc., are placed in cell-rows. Each Lichen, as a rule, has only one definite Algal-form for its gonidium.

The gonidia either lie together in a certain stratum between the cortex and the medullary layer (Fig. 131 g), or are scattered irregularly throughout the entire thallus (Fig. 132). The thallus is in the first instance termed “heteromerous,” in the second instance, “homoiomerous.” The Fungal-hyphæ embrace the gonidia and apply themselves closely to, or even penetrate them, and hence it has been difficult to decide whether the one cellular form does or does not develop from the other (Figs. 134, 135).

Fig. 132.—Collema microphyllum. Transverse section through the thallus; g Nostoc-chains; h hyphæ.

This theory regarding the symbiosis of Fungi and Algæ to form a Lichen is termed the Schwendenerian theory, after the first scientist who advanced it with any weight. It had been already indicated by De Bary, and further arguments in its support have at a later time been adduced by Bornet, Stahl, Treub, Frank, Bonnier, Alfr. Möller and others.

Fig. 133.—Ephebe pubescens. The apex of a branch of the thallus with two lateral branches (s): h its hyphæ; g the apical gonidium of the main branch.

Fig. 134.—Nostoc lichenoides, which is attached by a germinating thread (h) of Collema glaucescens.

Fig. 135.—A Germinating spore of Physcia parietina with Protococcus viridis. B Synalissa symphorea with Glæocapsa. C Cladonia furcata with Protococcus.

The thallus of the Lichen appears mainly under three forms:—

1. The Crustaceous, which adheres firmly to the substratum (bark, stone) throughout its entire surface, without being raised into any free patches or lobes. It has, in many instances, no definite outline, and hyphal-branches from it often penetrate deeply into the substratum. It grows at the circumference and sometimes dies away in the centre (Figs. 138, 139, 140).

2. The Foliaceous. This also lies flat upon the substratum, but is not firmly attached to and has a definite outline. It grows at the margin, and raises itself a little by free outgrowths and lobes (Fig. 141). The rhizoid-strands spring out from its whitish under surface (Fig. 131, r).

Fig. 136.—Portion of a hymenium: d a thin stratum on which the asci (s) are situated.

Fig. 137.—Spores of, a Cladonia, Lecanora and Pertusaria; b Bæomyces; c Sphinctrina; d, e, f various species of Parmelia; g, h Verrucaria in its younger and older condition; i, k species of Leptogium.

3. The Fruticose, which is attached to its substratum at a small point from which it projects freely, either erect or pendulous. It is more or less tufted, in the form of a bush (Figs. 142, 143). These three thallus-forms gradually pass over by many intermediate forms into one another.

Fig. 138.—Lecanora subfusca: a the bark on which it is situated; l the thallus; s the ascocarp; s’ an ascocarp.

Fig. 139.—Graphis (two species).

Fig. 140.—Pertusaria communis.

The Lichens, like other Ascomycetes, have very variously constructed ascospores (Fig. 137), which are enclosed in asci (Fig. 136), usually surrounded by paraphyses attached together. Furthermore they possess pycnidia (Fig. 141) containing numerous microconidia. These were formerly considered as organs of fructification, and were termed “spermatia,” and the pycnidia, “spermogonia.” Alfr. Möller proved, in 1887, that the microconidia are able to germinate and produce a mycelium with new conidia, just as in other Ascomycetes.

Vegetative Reproduction takes place by soredia, which to the naked eye appear as whitish powder on the surface of the thallus. They are small round bodies, formed by one or a group of gonidia, which are surrounded by a mass of felted hyphæ. After the rupture of the cortex they are set free, and readily carried by the wind to other places, where under favourable circumstances they establish a new thallus.

Fig. 141.—A A portion of the thallus of Parmelia parietina with ascocarps (a) and pycnidia (b). B A portion of the thallus of Cetraria islandica with pycnidia at the end of small lobes. C A lobe with pycnidia and ejected microconidia. (Magnified).

Geographical Distribution. The Lichens are the most hardy plants, and are the first to appear on hitherto bare rocks which they gradually disintegrate, and hence prepare the way for the growth of other plants. They are to be found from the Polar regions to the Equator; from the highest snow-free mountain-peaks down to the level of the sea; on the stems of trees; on rocks, soil, some even on inundated places; on stones in woodland streams, and on beaches; but they are never found upon rotten organic remains. Some grow gregariously in enormous masses, and form wide-stretching carpets, e.g. Reindeer Moss (Cladonia rangiferina), species of Cetraria and other fruticose Lichens.

Uses. On account of the cell-wall being composed of Lichenstarch (Lichenin), the Iceland-Lichen and Manna-Lichen (Lecanora esculenta) are used as food; the latter grows on stones, in the deserts of Asia and North Africa, and is often torn loose in large masses and carried away by the wind. The Reindeer-Lichen is not only the principal food of the reindeer, but it is also used in the manufacture of Danish brandy. Cetraria islandica (Lichen islandicus) is OFFICINAL. Colouring materials (lacmus, orseille, persio) are made from several species, especially from Roccella tinctoria (from the rocky coasts of the Mediterranean). Parmelia saxatilis and particularly Lecanora tartarea are used for colouring purposes in the Northern countries.