THE ASPERGILLUS USTUS GROUP 



173 



Upon malt agar, colonies frequentl,y heavier sporing and conidial heads 

 generally tending to run to dull gray-green shades rather than brown. 



Very common in soil and decaying vegetation. Species diagnosis repre- 

 sents a composite based upon many isolations from this country and abroad. 



B 



D 



Fig. 48. Aspergillus ustus: cultures growing upon Czapek's solution agar at room 

 temperature, 10 days. A, Strain XRRL No. 275 characterized by loose floccose 

 colonies and moderate sporulation. B, Strain NRRL No. 278 characterized by 

 heavier spore production and the presence of abundant hiille cells. C, A. ustus var. 

 laevis, NRRL No. 1852, characterized by loose floccose colonies and conidial heads 

 often near brick red in color. D, Strain NRRL No. 1974 characterized by the pro- 

 duction of very abundant hiille cells in concentric zones. 



Individual strains differ markedly in their general habit and colony colora- 

 tion, in the color of their fruiting structures, in the marking and coloration 

 of their conidia, in the presence or absence of hiille cells, and in the form of 

 these structures when present. By a deliberate selection of strains, one 

 can find sufficient difference to warrant the assignment of specific designa- 



