656 A MANUAL OF THE PENICILLIA 



but differing markedly in color and texture (fig. 165E), approximating 

 olive yellow to olive ocher (Ridgway, PL XXX), appearing somewhat 

 granular or tufted, especially in marginal areas, and consisting of a com- 

 paratively thin, closely interwoven network of yellow encrusted, much- 

 branched, sterile hyphae enmeshing and largely obscuring numerous conid- 

 ial structures; penicilli biverticillate and symmetrical, short and very com- 

 pact (fig. 165F), bearing metulae in large crowded clusters of 12 to 15 or 

 more, individually measuring about 7 to 8ju by 1.5 to 1.8ju; sterigmata in 

 verticils of 6 to 8, about 7.5 to 9.0^ by 1.5/x, lanceolate with characteris- 

 tically tapered tips; metulae and sterigmata usually yellowish green in 

 color; conidia elliptical to subglobose, mostly 2.4 to 2.8m by 2.0 to 2.5m with 

 walls comparatively thin, smooth or nearly so, in yellow-green shades. 



The varietal name is based upon a characteristic yellow coloration upon 

 certain media, including malt extract and Saboraud's agars. The variety 

 differs from the species principally in the production of greatly increased 

 amounts of yellow encrusted mycelium, and in the production of more com- 

 pact penicilli consisting of substantially greater numbers of metulae and 

 sterigmata. 



Growth is more luxuriant when cultivated upon media containing am- 

 monium instead of nitrate nitrogen, but unlike the species, growth upon 

 this type of substrate does not equal that upon malt agar. The variety, 

 however, obviously possesses the same basic nutritional deficiencies as the 

 species. 



The variety is represented by NRRL 1074, received in 1934 from R. W. 

 Davidson, Division of Forest Pathology, Bureau of Plant Industry. The 

 strain was initially diagnosed as Penicillium tardum Thom upon the basis 

 of its symmetrically biverticillate penicilli and its restricted growth on 

 Czapek's agar. The subsequent discovery and recognition of P. diversum 

 Raper and Fennell, showed the true relationship of the variety to be with 

 this species rather than with P. tardum Thom. 



Occurrence and Significance 



Members of the Penicillium rugulosum series appear to be abundant in 

 all soils, and in addition commonly occur upon a wide variety of organic 

 substrata including vegetable materials, stored grain, leather, tentage, and 

 various other types of military equipment exposed to weathering processes. 

 Like the P. citrinum series, these molds seem to be especially adapted to 

 growth under conditions of limited nutrients and variable moisture. Their 

 actual role in decomposition processes has received comparatively little 

 attention. 



McBeth and Scales (1913) and Scales (1915) reported Penicillium rugu- 

 losum as one of several species able to decompose cellulose. Thom (1930) 



