MORPHOLOGY AND CLASSIFICATION 



US 



cies. The common aspergilU belong here. The basidiomycetes 

 are characterized by the occurrence of a spore-bearing cell, the 

 basidium, which bears four protuberances called sterigmata 

 (singular sterigma) upon each of which is a single spore. Mush- 

 rooms and puff-balls belong to this group. Besides these three 

 well-defined classes, there are many kinds of molds and fungi con- 

 cerning which definite knowledge is still too incomplete for them 

 to be finally placed. These are designated as imperfect fungi, 



Fig. 62. — Yeast cells stained with fuchsin. ( Xiooo.) 



Fungi imperfecti, or perhaps best by the class name, Hypho- 

 mycetes. In these forms, zygospores and ascospores are un- 

 known; the hyphae are often septate. Reproduction takes place 

 by the formation of conidia only. These are oval or rounded 

 cells produced by transverse division of a filament, usually as a 

 row of conidia at the end of a hypha. The common oidium and 

 many parasitic molds belong in this class. The molds^ are es- 

 pecially important as causes of disease in plants. Relatively few 

 1 For fuller discussion of molds in general see Marshall, Microbiology, article by 

 Thorn. 

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