THE TRICHOPHYTONEAE 385 



Another technique for identification arises from the work of 

 Davidson, Dowding, and Buller (1932). They observed that hy- 

 phal fusions or anastomoses occur between hvphae of the same 

 mycelium or between mvcelia of different origin but of the same 

 species, and that no hyphal fusions form between mvcelia of dif- 

 ferent species. If, then, the investigator has stock cultures whose 

 identity is known, it becomes possible by suitable pairings to estab- 

 lish the identity of unknown isolates. In their studies Davidson, 

 Dowding, and Buller employed Micros porinn audoiiini, M. lano- 

 sinn, and Trichophytum gypsenm. 



Relationship of ringworm fungi with other fungi. Evi- 

 dence has been presented to show that the ringworm fungi are 

 conidial forms of Gymnoascaceae and that they have lost their 

 ability to produce asci. Some of this evidence includes the fact 

 that Ctenomyces servants, growing naturally on feathers, possesses 

 as peridial ornaments spiral hyphae that are like those of certain 

 species of small-spored Trichophyton, and that it forms aleuro- 

 spores and spindles in culture. Nannizzi (1926) is among those 

 who would classify the ringworm fungi with the Gymnoascaceae. 

 He maintained that they should be grown on hair, feathers, horn, 

 or skin and that the morphologic structures developed on syn- 

 thetic media are all abnormalities. When he cultivated Achorion 

 gypsenm on these animal decidua, he reported the development 

 of asci and ascospores like those of Gymnoascus. Tate (1929) 

 was unable, however, to confirm Nannizzi's findings; moreover 

 they remain without confirmation for other species, and hence it 

 must be concluded that all these problems of relationships require 

 further study. 



Pleomorphism. The phenomena of production of physiologi- 

 cal species by fungi and of sectoring, saltation, and mutation were 

 discussed in Chapter 7. The term pleomorphism is not to be asso- 

 ciated with these phenomena; it applies to a peculiar and confus- 

 ing change that is especially prevalent among ringworm fungi. 

 When these fungi are grown on sugar-containing media and have 

 reached their maximum development, which is usually attained 

 after 4 to 6 weeks, white, downy tufts suddenly appear on the 

 surface of the mature colonies, suggesting the presence of a sur- 

 face contaminant. These tufts grow rapidly, enveloping the 

 whole surface and spreading beyond the margin of the primary 

 colony, until a mantle of pure white, downy mycelium envelops 



