GENERAL MORPHOLOGY OP FUNGI 25 



Phycomycetes. — This group in its more primitive members seems distantly 

 related to the Flagellata of the Protozoa. Most of the members have a vegeta- 

 tive body of mycelium and in all but one order reproduce by a flagellated 

 body. Most of the group are saprophytes or parasites on plants except a few 

 facultative parasites of fish or invertebrates. The only group at present known 

 to produce human parasites is the Mucorales which will be treated later in 

 the appropriate chapter. 



Ascomycetes. — The more primitive members show distant relationships to 

 the higher Phycomycetes on the one hand and to the Ehodophyceae (Red 

 Algae) on the other. After a half century of bitter controversy on this ques- 

 tion, there is still little agreement. Here the vegetative body is a typically 

 uninucleate, septate mycelium and sexual reproduction occurs by means of 

 cells produced within an ascus, following meiosis in all forms where this has 

 been carefully studied. Of the twenty orders into which this group is usually 

 divided, members of only two, the most aberrant and primitive (or degener- 

 ate), have been shown to cause human disease. The bulk of the group are 

 saprophytes or parasites of the leaves and bark of plants, while the most 

 highly specialized (Laboulbeniales) are at present known only as parasites 

 of living insects. 



Basidiomycetes. — While the life cycle shows a certain parallelism to that 

 of the higher Phycomycetes and the Ascomycetes, it is difficult to assign to 

 these any very close relationship with other groups. The vegetative body 

 again consists of uninucleate or binucleate mycelium, forming a conspicuous 

 fructification on which the reproductive structures are borne. Reproduction 

 occurs by means of basidiospores. So far as is known the group is saprophytic 

 on decaying vegetable matter in the conspicuous species, such as the mush- 

 rooms, punks, puffballs, etc., or parasitic, usually on leaves, in the Uredinales 

 (rusts) and Ustilaginales (smuts). 



Fungi Imperfecti. — These are a large group, artificially classified together 

 while we await more knowledge of their life history. The greater part, whose 

 life history has been discovered, has been found to be Ascomycetes, but it is 

 never safe to predict that several members of a given genus of Fungi Im- 

 perfecti will necessarily belong to the same genus of Ascomycetes or even 

 will be Ascomycetes; e.g., when Oedocephalum was carefully studied, one 

 species was found to be a Phycomyeete, another an Ascomycete, and a third a 

 Basidiomycete. Various subdivisions have been proposed, but none has proved 

 altogether satisfactory. Further considerations may well be delayed to a 

 subsequent chapter (p. 665). 



In the following chapters only those orders will be discussed in which 

 mammalian pathogens have been found, and the reader is referred to Gau- 

 mann and Dodge (1928) for information on other groups. 



BIBLIOGRAPHY 



The following bibliography includes references to early work in which 

 it is difficult or impossible to be sure of the group of fungi involved, also gen- 



