ASYMMETRICA-VELUTINA 381 



which break off readily as crusts when mature; penicilli are essentially like 

 those produced upon Czapek, 



Strains of Penicillium oxalicum commonly show progressive variation 

 under continued laboratory cultivation, and in time produce colonies that 

 are loose textured, light sporing and more or less floccose or even funiculose 

 (fig. lOOE), and which usually exhibit a flesh to light pink coloration, at 

 least in more strictly mycelial areas. Fruiting structures, although rela- 

 tively few in number, generally remain essentially typical in pattern with 

 the form and dimensions of conidia and spore bearing parts unchanged. 



Species diagnosis is based upon typical cultures contained in the NRRL 

 Collection such as NRRL 790, received in 1934 from S. A. Hall as a strain 

 of "Danish Roquefort" mold; NRRL 1836, isolated in 1942 from South 

 Carolina soil; NRRL 2139, isolated from moldy leather and received in 

 September 1944 from T. C. Cordon, Eastern Regional Research Labora- 

 tory, Wj^ndmoor, Pennsylvania; and innumerable other strains isolated 

 from soils and various organic substrates undergoing slow aerobic decom- 

 position. 



Currie and Thom's description was based upon Thom's culture No. 103 

 (NRRL 787) as type. In 1915 this strain produced velvety, heavily sporing 

 colonies conforming with the species description as given above, but during 

 the more than 30-year period that it has been maintained in laboratory 

 culture it has exhibited a gradual and progressive variation away from the 

 original (fig. lOOE) until today it could hardly be assigned to this species 

 except for the fact that it has been under continual observation and that 

 its conidial structures, although sparsely produced, still conform in general 

 to those of more typical strains. Other cultures when maintained in the 

 laboratory over considerable periods show similar variation and we are led 

 to believe that the tendency of strains to become more floccose and less 

 heavily sporing represents a true species character. 



Penicillium oxalicum is cosmopolitan in its habitats and apparently 

 world-wide in distribution. It is especially common in soil and upon plant 

 residues undergoing slow decomposition. 



Penicillium atram,entosum Thom, in U. S. Dept. Agr., Bur. Anim. Ind., Bui. 

 118,pp. 65-66, fig. 24. 1910. Emended in Thom, The Penicillia, 



pp. 251-252. 1930 



Colonies upon Czapek's solution agar spreading, attaining a diameter of 

 5.0 to 6.0 cm. in 10 days at room temperature, comparatively thin, heavily 

 sporing, velvety except for the presence of limited sterile hyphae in central 

 colony areas, strongly furrowed in a predominantly radial pattern but with 

 less regularity in central than in submarginal zones (fig. 101 A), marginal 

 area 2.0 to 3.0 mm. wide, thin, white to pale blue-green with the develop- 



