58 MORPHOLOGY AND CULTURE OF MICROORGANISMS 



the mycelium and substrata; colonies of Alternaria often become almost 

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

 except for the specialist. 



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

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

 vegetables, manure, etc. Colonies of the species are colorless, have 



FIG. 40. Oidium lactis. a, b, Dichotomous branching of growing hyphae; c, d, 

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

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

 cell; h, branching chain of oidia; k, I, m, n, o, p, s, types 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. 



vegetative mycelium entirely submerged, become powdery-white with 

 spores when mature, liquefy gelatin, and produce a strong character- 

 istic odor (Fig. 40). Microscopically the species is recognized by dicho- 

 tomous branching of the hyphae at the margin of the rapidly growing 

 colonies, and by the spores or oidia which are abruptly cylindrical, 

 varying with conditions in length and diameter and produced both 



