606 - Heredity and Evolution 



forth, and through their pathogenic effects 

 upon various plants and animals. However, 

 the sac fungi also do much good. Various 

 species of Aspergillus are used in the produc- 

 tion of alcohol, citric acid, and other organic 

 compounds; Penicilliiim roqueforti and cam- 

 emberti contribute distinctive flavors to 

 roquefort and camembert cheeses," and Petri- 

 cillium notatum, which produces the anti- 

 biotic, penicillin, has been extremely valu- 

 able in helping to cure mastoiditis, syphilis, 

 gonorrhea, and cjuite a few other previously 

 serious infections. 



The Basidiomycetes (Basidium, or Club Fungi). 

 This other large (25,000 species) class of the 

 Eumycophyta also includes a number of fa- 

 miliar and important fungi. Among the free- 

 living, saprophytic species are the mushrooms 

 (Fig. 31-13), the puffballs (Fig. 31-14), and 

 the bracket fungi. And among the patho- 

 genic species there are the rusts and the 

 smuts. 



A distinctive feature of the Basidiomycetes 

 is their unique method of forming spores. 

 Following sexual reproduction, a number of 

 large club-shaped diploid cells, each called a 

 basidium, are formed on certain reproduc- 



tive hyphae (Fig. 31-15). The diploid nucleus 

 of the basidial cell divides twice (meiosis), 

 giving rise to four haploid nuclei. These 

 nuclei then migrate out into the four spore 

 cells (basidiospores) that are budded off at 

 the end of the basidial cell (Fig. 31-15). Each 

 haploid basidiospore can give rise to a new 

 mycelium, in which all the cells are haploid; 

 and the haploid status of the species persists 

 until sexual reproduction occurs again. 



Usually the reproductive hyphae, upon 

 which the basidia and basidiospores are 

 formed, are organized into fruiting organs, 

 called sporophores, which display a definite 

 shape and color in each of the species. Thus 

 it is possible to recognize each species on the 

 basis of its sporophore — as is shown for the 

 common edible mushroom in Figure 31-13. 

 It should be remembered, however, that the 

 mycelium of the species, which lies buried 

 in the humus-laden soil, or in some other 

 organically rich medium, must have grown 

 for a long time before the sporophore sud- 

 denly "mushrooms" and thrusts itself into 

 sight. 



Almost 200 edible varieties of mushrooms 

 are known. There are, however, about 30 



Fig. 31-13. The commonly cultivated edible mushroom (Psalliota campesrris) is one 

 of the Basidiomycetes, or club fungi. This is a flashlight photo, taken in a mush- 

 room cellar. (From The Plant World.) 



