298 



YEASTS AND YEAST-LIKE FUNGI 



probably should not be considered as a part of the Cryptococcaceae 

 at all. The mycelium is definitely a true mycelium, blastospores are 

 scarcely if ever produced, but arthrospores are formed regularly. In 

 liquid media the best-known species Geotrichum candidum, produces 

 a rather firm, felt-like mass, pure white in color. On solid media this 

 is at first rather firmly adherent. Later it becomes soft and creamy. 

 Microscopic examination shows both septate branched mycelium and 

 numerous large square-ended arthrospores, the latter frequently 



joined together in short chains at 

 alternate corners in zig-zag ar- 

 rangement. The aerial arthro- 

 spores are more rounded and are 

 called conidia by some workers 

 and are distinguished from the 

 cylindrical submerged oidia, but 

 many workers, realizing that 

 there are all gradations, make 

 no such differentiations. As 

 arthrospores become numerous, 

 the growth becomes soft and 

 creamy and takes on the ap- 

 pearance and odor of an ordi- 

 nary yeast culture. The frag- 

 mentation of the mycelium into 

 arthrospores has been observed 

 by means of motion pictures. 

 A word about nomenclature. G. candidum is probably most often 

 known as Oidium lactis, and nearly as often as Oospora lactis. The 

 term Oidium to the general mycologist or phytopathologist means the 

 imperfect stage of certain ascomycetous fungi, the powdery mildews. 

 These are exclusively organisms parasitic on plants and they have 

 true conidia borne on conidiophores. G. candidum has only super- 

 ficial resemblance to these organisms, and hence Oidium lactis has 

 to be placed in another genus. Geotrichum was created in 1809 for 

 this very species as G. candidum. Geotrichum antedates Oospora 

 (which itself is used in many different senses) by 24 years. Rarely 

 Mycoderma lactis is also used but, as stated earlier, this is now 

 generally regarded as a misuse of the term IVIycoderma. We have 

 no choice but to adopt the earlier term G. candidum which is becom- 

 ing more familiar in the field of applied mycology. See Chapter VIII 

 for a discussion of the industrial importance of this fungus. 



Fig. 119. Geotrichum candidum, show- 

 ing development of oidia. Photomi- 

 crograph by dark field illumination. 



