ZYGOMYCETES 337 



zygosperm gives rise directly to a promycele bearing the characteristic 

 spores, and these in turn produce on germination a mycele which bears 

 spores again, and ultimately a zygosperm. It has been observed in an 

 artificially nourished individual, that the germinating zygosperm at once 

 produced a mycele which subsequently bore spores without the inter- 

 vention of the promycele stage. In another instance (Sporodinia grandis. 

 Link) zygosperms have been observed on a mycele which arose from a 

 spore, before the production of sporophores upon it ; while it sometimes 

 happens in this species that a zygosperm is produced on a mycele arising 

 directly from a zygosperm without the intervention of spores at all. But 

 in the great majority of cases the production of spores precedes the 

 formation of a zygosperm on the same mycele. In many species the 

 zygosperms are of rare occurrence, and an indefinite number of succes- 

 sive spore-bearing generations come between zygosperm and zygosperm. 

 Throughout the whole order spores are produced in vastly greater 

 numbers than zygosperms. Syzygites (Ehrenb.) is the generic name given 

 to certain forms of doubtful affinity which produce, so far as is known, 

 zygosperms alone. 



Sub-order i : Mucore.e. — The members of this group are for the 

 most part saprophytes on the excrement of animals, fruits, bread, 

 saccharine fluids, (S:c. The thallus-hyphse are relatively large and much 

 ramified. The conjugating hyphse arise either as branches of the 

 mycele or on special hyph^ somewhat resembling sporangiophores, 

 their place of origin being, in different instances, in either morphological 

 or merely local approximation to each other. At an early stage of 

 development they come into contact by their apices, and a firm connec- 

 tion between the two is established. Thus joined the development of 

 each goes on, and soon a transverse wall cuts off the apical portion of 

 each. This portion is a gamete^ and the rest of the hypha, generally 

 club-shaped, its suspensor. A pore next appears in the centre of the 

 original wall separating the two gametes, and gradually the whole wall 

 disappears and the contents conjugate. The zygosperm thus formed 

 increases in size, drawing upon the contents of the suspensors. The 

 protoplasm becomes dense, and the fatty contents gather into a large drop. 

 The wall commonly becomes covered externally with warts or spines at 

 all points except where the suspensors are attached. The form of the 

 whole is roundish or drum-shaped, the smooth walls adjoining the sus- 

 pensors corresponding with the sides of the drum. The wall is divided 

 into two coats, the outer one {extine) brown or black, and the inner one 

 {intine) stratified, and either entering the corrugations of the extine or 

 remaining smooth along the surface of contact with it. The suspensors 

 usually remain in statu quo, but in Rhizopus nigricans (Ehrenb.), where 



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