MOLDS. 25 



and spores are at first colorless, but later dark colored to almost black, 

 with spores becoming two-celled in very old cultures. 



Cladosporium herbarum is the commonest species encountered.* Col- 

 onies in culture media differ so greatly in structure from those upon natural 

 substrata as to make identification of species questionable. Fig. 6. 

 Much confusion is therefore found in the use of the names of species 

 of Cladosporium and the related genus, Hormodendron, which is sepa- 

 rated by some. 



ALTERNARIA AND FUSARIUM. The frequent occurrence of species of 

 A Iternaria and Fusarium in cultures demands that the generic characters 

 be recognized. Both, as a rule, produce abundant growth with a tendency 

 to over-run cultures of other forms (Figs. 8 and 9). The spores of Alter - 

 naria are brown, Indian-club form, muriform (divided into several cells by 

 longitudinal as well as cross walls), and are connected together into 

 chains (Fig. 8). The spores of Fusarium are colorless, either straight 

 or sickle- or crescent-shaped, divided into several cells by cross walls 

 occur singly or adhere into masses on the tips of the fertile branchlets 

 "The morphology of colonies in culture varies widely from the descrip- 

 tions of the same species under natural conditions. Species of Fusa- 

 rium frequently produce bright colors in 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 very frequently in decaying vege- 

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

 mycelium entirely submerged, become powdery white with spores when 

 mature, liquefy gelatin, and produce a strong characteristic odor (Fig. 10). 

 Microscopically the species is recognized by dichotomous branching of 

 the hyphae at the margin of the colonies, and by the spores or oidia which 

 are abruptly cylindrical, varying with conditions in length and diameter 

 and produced both above and below the surface of the substratum in 

 long chains which break up readily. At times the whole mycelium ap- 

 pears to break up into oidia. Oidium lactis is a factor in the ripening 

 of many kinds of cheese: Limburg, Harz, Camembert, Gorgonzola, etc. 

 Its activity is associated with strong odor and taste. 



MONILIA. Monilia Candida (Bonorden), Hansen. The line be- 



* This species has been shown to be a conidial form of Sph&rella tulasnei Janczewski, but 

 the bacteriological student will meet only the conidial stage. 



