INTRODUCTION 15 



system. The imperfect forms of which it consists are separated 

 by an artificial classification based largely on spore characters. 

 When one of them is proved to be the imperfect stage of a known 

 member of the Phycomycetes, Ascomycetes, or Basidiomycetes it 

 passes automatically to that group, and bears thereafter the 

 name apphed to the perfect stage. It is to be expected that 

 in time hundreds of such transfers will be made. Certain forms, 

 which are properly speaking Fungi Imperfecti, have never been 

 included in the group because their characters are such as to 

 indicate clearly their actual relationships. Members of the 

 Mucorales known only in the asexual (sporangial) condition, 

 and unconnected stages of rusts (Uredinales) belonging to the 

 form genera Aecidium, Caeoma,Peridermium,Roestelia, and Uredo 

 fall in this category. 



The outstanding characters of the Phycomycetes, Ascomycetes, 

 and Basidiomycetes will now be indicated briefly. The Phycomy- 

 cetes embrace the lower fungi treated in this book. A general 

 discussion of the group is given in the following chapter. The 

 Ascomycetes and Basidiomycetes are called the higher fungi. 

 Certain authors restrict the name Eumycetes to them. 



The Phycomycetes viewed in their entirety are a diverse group. 

 The primitive members of the class are chiefly aquatic, while the 

 more recent are terrestrial. The thallus in the lower forms is 

 characteristically simple and inconspicuous. In the higher it 

 develops as a profusely branching mycelium, which is usually 

 more evident than the reproductive bodies. The mycelium is 

 usually coenocytic (non-septate and plurinucleate), but in some 

 forms, chiefly the highest, tends to develop septa in age or may 

 even be normally septate from the beginning. In practically all 

 cases septa are formed in the delimitation of the reproductive 

 cells. Sexual organs are commonly present and usually func- 

 tional. The product of sexuahty is usually a spore (oospore or 

 zygospore). In a few known cases motile sex cells (gametes) 

 fuse in pairs to form motile zygotes. In a single genus, Mono- 

 blepharis, ciliated antherozoids fertilize the female cell. In 

 some species the sexual cells are no longer functional. In others, 

 one or both cells have been suppressed. Asexual reproduction 

 occurs typically by means of spores (sporangiospores) borne in 

 a sac called the sporangium. The sporangiospores in the lower 

 forms are usually motile (zoospores, swarmspores), but in the 

 higher are usually non-motile (aplanospores) . In many cases, 



