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.