56 



MORPHOLOGY AND CULTURE OF MICROORGANISMS 



colorless, either straight or sickle- or crescent-shaped, divided into 

 several cells by cross- walls occur singly or adhere in masses on the tips 

 of the fertile branchlets. The morphology of colonies in culture varies 

 widely from the descriptions of the same species under natural condi- 

 tions. Species of Fusarium frequently produce bright colors in the 

 mycelium and substrata; colonies of AUernaria often become almost 

 black. Identification of species in cultures is thus far impossible, 

 except for the specialist. 



Fig. 39. — Oidium lactis. a, h, Dichotomous branching of growing hyphse; c, d, 

 g, simple chains of oidia breaking through substratum at dotted line x-y, dotted 

 portions submerged; e,/, chains of oidia from a branching out-growth of a submerged 

 cell; h, branching chain of oidia; k, I, m, n, 0, p, s, tjrpes of germination of oidia under 

 varying conditions; t, diagram of a portion of a colony showing habit of Oidium 

 lactis as seen in culture media. (From Bull. 82, Bur. Animal Industry, U. S. Dept. 

 Agr.) 



Oidium. — Oidium (Oospora) lactis is universally found in cultures 

 from milk and milk-products and very frequently in decaying vege- 

 tables, manure, etc. Colonies of the species are colorless, have vege- 

 tative mycelium entirely submerged, become powdery white with 



