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.