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.

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.

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.

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.

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.

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.

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.

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).

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.

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.

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.

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.

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.

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.

Sub-Family 2. Stictidales.

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

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.

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.

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.

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.

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.

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.

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).

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).

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.