TRICHOPHYTONEAE 



449 



scarcely visible ; the plasma cells are frequently numerous. It differs from 

 kerion in being- slow in development and very chronic. 



Since the characters of the giant colony seem quite distinctive and have 

 been much used in systematic studies, they may be reviewed briefly, although 

 for details the reader is referred to the descriptions of the various species. 

 Up to the present, the aim has been to cultivate the species on Sabouraud's 

 maltose or glucose agar or on s.ome modification which will produce closely 

 similar colonies, since some of the luxuriance of the colonies, upon which 

 Sabouraud's original descriptions were based, seems to have been due to im- 

 purities in his crude maltose and glucose. In general, the species which are 

 more restricted as to host and method of parasitism are less luxuriant in 

 growth upon artificial media, while those growing easily on a large variety of 

 hosts, and producing more active suppuration, are luxuriant. 



Fig. 78. — Mycelium. 1, Microsporuin Audouini; 2, MegatricJiophyton equinum; S, M. 

 fen'ugineum; i, Favotrichophyton ochraceum; 5, EiXtdodermophyton tropicale; 6, Acladium 

 VasteUanii. (After Ota & Langeron 1923.) 



The colony may be either crateriform, acuminate, or cerebriform. Char- 

 acteristic and conspicuous radial furrows or folds are common, while con- 

 centric furrows or zones are rare. The appearance of the surface is largely 

 dependent on the nature of the reproductive organs produced. Sterile myce- 

 lium is very loose and cottony as seen in pleomorphic mycelia (see p. 456). 

 Somewhat denser and feltlike is the mycelium when the fusiform spores are 

 predominant. Where the aleurospores are predominant, the surface is powderj^ 

 to chalky. When only chlamydospores are produced, the colom- is moist, 

 glabrous, and almost yeastlike. 



The mycelium of the less degenerate forms is usually dimorphic. The 

 primary mycelium which bears the closterospore or the chlamydospore, is 

 septate, relatively coarse, 4-5ft in diameter, with 5 nuclei in mature cells, while 



