Ascobolus ([Fig. 43]) is a small, disc-shaped fungus, growing on horse dung. By keeping some of this covered with a bell jar for a week or two, so as to retain the moisture, at the end of this time a large crop of the fungus will probably have made its appearance. The part visible is the spore fruit ([Fig. 43], A), of a light brownish color, and about as big as a pin-head.
Its development may be readily followed by teasing out in water the youngest specimens that can be found, taking care to take up a little of the substratum with it, as the earliest stages are too small to be visible to the naked eye. The spore fruits arise from filaments not unlike those of the mildews, and are preceded by the formation of an archicarp composed of several cells, and readily seen through the walls of the young fruit ([Fig. 43], B). In the study of the early stages, a potash solution will be found useful in rendering them transparent.
The young fruit has much the same structure as that of the mildews, but the spore sacs are much more numerous, and there are special sterile filaments developed between them. If the young spore fruit is treated with chlor-iodide of zinc, it is rendered quite transparent, and the young spore sacs colored a beautiful blue, so that they are readily distinguishable.
Fig. 43.—A, a small cup fungus (Ascobolus), × 5. B, young spore fruit, × 300. ar. archicarp. C, an older one, × 150. ar. archicarp. sp. young spore sacs. D, section through a full-grown spore fruit (partly diagrammatic), × 25. sp. spore sacs. E, development of spore sacs and spores: i–iii, × 300; iv, × 150. F, ripe spores. G, a sterile filament (paraphysis), × 300. H, large scarlet cup fungus (Peziza), natural size.
The development of the spore sacs may be traced by carefully crushing the young spore fruits in water. The young spore sacs ([Fig. 43], E i) are colorless, with granular protoplasm, in which a nucleus can often be easily seen. The nucleus subsequently divides repeatedly, until there are eight nuclei, about which the protoplasm collects to form as many oval masses, each of which develops a wall and becomes a spore (Figs. ii–iv). These are imbedded in protoplasm, which is at first granular, but afterwards becomes almost transparent. As the spores ripen, the wall acquires a beautiful violet-purple color, changing later to a dark purple-brown, and marked with irregular longitudinal ridges ([Fig. 43], F). The full-grown spore sacs ([Fig. 43], E, W) are oblong in shape, and attached by a short stalk. The sterile filaments between them often become curiously enlarged at the end (G). As the spore fruit ripens, it opens at the top, and spreads out so as to expose the spore sacs as they discharge their contents ([Fig. 43], D).
Of the larger cup fungi, those belonging to the genus Peziza ([Fig. 43], H) are common, growing on bits of rotten wood on the ground in woods. They are sometimes bright scarlet or orange-red, and very showy. Another curious form is the morel (Morchella), common in the spring in dry woods. It is stalked like a mushroom, but the surface of the conical cap is honeycombed with shallow depressions, lined with the spore sacs.
Order Lichenes.
Under the name of lichens are comprised a large number of fungi, differing a good deal in structure, but most of them not unlike the cup fungi. They are, with few exceptions, parasitic upon various forms of algæ, with which they are so intimately associated as to form apparently a single plant. They grow everywhere on exposed rocks, on the ground, trunks of trees, fences, etc., and are found pretty much the world over. Among the commonest of plants are the lichens of the genus Parmelia ([Fig. 44], A), growing everywhere on tree trunks, wooden fences, etc., forming gray, flattened expansions, with much indented and curled margins. When dry, the plant is quite brittle, but on moistening becomes flexible, and at the same time more or less decidedly green in color. The lower surface is white or brown, and often develops root-like processes by which it is fastened to the substratum. Sometimes small fragments of the plant become detached in such numbers as to form a grayish powder over certain portions of it. These, when supplied with sufficient moisture, will quickly produce new individuals.