Fig. 46.—Branch of a plum-tree attacked by black knot. Natural size.
Not infrequently in this form, as well as in other lichens, special cavities, known as spermogonia ([Fig. 44], D), are found, in which excessively small spores are produced, which have been claimed to be male reproductive cells, but the latest investigations do not support this theory.
The last group of the Ascomycetes are the “black fungi,” Pyrenomycetes, represented by the black knot of cherry and plum trees, shown in [Figure 46]. They are mainly distinguished from the cup fungi by producing their spore sacs in closed cavities. Some are parasites; others live on dead wood, leaves, etc., forming very hard masses, generally black in color, giving them their common name. Owing to the hardness of the masses, they are very difficult to manipulate; and, as the structure is not essentially different from that of the Discomycetes, the details will not be entered into here.
Of the parasitic forms, one of the best known is the “ergot” of rye, more or less used in medicine. Other forms are known that attack insects, particularly caterpillars, which are killed by their attacks.
CHAPTER X.
Fungi—Continued.
Class Basidiomycetes.
The Basidiomycetes include the largest and most highly developed of the fungi, among which are many familiar forms, such as the mushrooms, toadstools, puff-balls, etc. Besides these large and familiar forms, there are other simpler and smaller ones that, according to the latest investigations, are probably related to them, though formerly regarded as constituting a distinct group. The most generally known of these lower Basidiomycetes are the so-called rusts. The larger Basidiomycetes are for the most part saprophytes, living in decaying vegetable matter, but a few are true parasites upon trees and others of the flowering plants.
All of the group are characterized by the production of spores at the top of special cells known as basidia,[8] the number produced upon a single basidium varying from a single one to several.