MOLDS 20 



One genus is, however, constantly found. The commonest species of 

 Aspergillus produces bright yellow, globose fruiting bodies, called 

 feritkecia, filled with asci. These are borne upon the surface of the 

 substratum and often give a yellow color to the colony by their abund- 

 ance. Such perithecia consist of the ascogenous cells and the asci 

 produced by them, about which a more or less completely closed sac 

 or wall has been formed, by the development of the sterile cells ad- 

 jacent to the fruiting ones. 



Basidiomycetes. — In the Basidiomycetes there is still further reduc- 

 tion of the evidences of sexuality. In one border group, the rusts, 

 sexual processes have been shown to be more or less developed. In 

 the typical Basidiomycetes sexuality is reduced to a fusion of the 

 nuclei in certain binucleate cells. The typical structure is the basid- 

 ium, a spore-bearing cell characteristically producing at its apex 

 four protuberances called sterigmata (singular, sterigma), each bearing 

 a single spore. These basidia are grouped into many kinds of fruit 

 bodies, from occurrence here and there upon a loose web of hj^phae 

 to dense columnar areas covering the gills of the mushrooms or lining 

 the cavities of the puffballs. Very few of these species occur in bac- 

 teriological studies. 



Imperpect Fungi. — ^A very large number of species are known 

 which have never been seen to produce the characteristic fruits of the 

 great groups. These are brought together and described as form- 

 genera by their method of asexual spore formation. From the lack of 

 the organs used in classifying the other groups, these are called the im- 

 perfect fungi and their grouping regarded only as temporary, a con- 

 venience for the identification of materials. These include many forms 

 of economic importance, and many of the species most frequently 

 met in bacteriological work. Sometimes one species of a large group 

 produces a perfect form while no other species can be induced to do 

 so. Some of these species undoubtedly represent stages of perfect 

 fungi whose perfect forms simply are not recognized as connected with 

 these; others reproduce for an indefinite number of generations by 

 conidia. Such cases do not appear to need the perfect form and hence 

 apparently have, in some cases, lost the power to produce it. 



As found in nature all these forms are parasitic, saprophytic, or 

 capable of both modes of life. All depend more or less completely 

 upon organic matter for nourishment. Great diversity exists, how- 



