MOLDS 39 



materials; the antheridium is much smaller, penetrates and fertilizes 

 the oospore, which afterward develops into a thick- walled resting spore. 

 The very destructive downy mildews belong to this group. 



ASCOMYCETES. In this great group sexuality was denied until recent 

 years, but has been proved in cases enough to establish a presumption of 

 more general occurrence. The characteristic structure of the group is 

 the ascus, a sac containing, when ripe, typically eight spores, some- 

 times a less number by the failure of some to develop, sometimes a larger 

 number, usually some multiple of eight. The ascus when sexuality is 

 known is developed subsequent to fertilization, not directly from an 

 egg cell. The group presents a great variety of fruiting masses pro- 

 duced in connection with the asci. The simplest forms are loose webs 

 of hyphae enmeshing a few asci; other forms show clubs, cups, flask 

 forms, crusted areas, the type of mass in each case being characteristic 

 of the family, genus and species represented. Only a few of many 

 thousands of these forms are encountered in bacteriological work. 

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

 Aspergillus produces bright yellow, globose fruiting bodies, called 

 perithecia (singular, perithecium) , filled with asci. These are borne upon 

 the surface of the substratum and often give a yellow color to the colony 

 by their abundance. Such perithecia consist of the ascogenous ceils 

 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 adjacent to the fruiting ones. 



BASIDIOMYCETES. In the Basidiomycetcs there is still further reduc- 

 tion of the evidences of sexuality. 



In some sections of this group an essential sexuality has been corre- 

 lated with the fusion of nuclei at stages of life history characteristic 

 for the particular sections of the group. Such fusion seems to underlie 

 the development of the typical faint body, although it has only been 

 demonstrated in a small number of species. The typical structure is 

 the basidiuniy a spore-bearing cell characteristically producing four 

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

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

 varying from occurrence here and there upon a loose web of hyphae to 

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

 cavities of the puffballs. Very few of these species are encountered in 

 bacteriological studies. 



