350 A MANUAL OF THE PENICILLIA 



(6) Nutrient Deficiency Mutants: Cultures are occasionally encountered 

 which grow very sparsely upon Czapek's solution agar but grow luxuriantly, 

 sporulate heavily, and in general duplicate well recognized species upon 

 malt and steep agars. Such a strain of Pemcillium citrinum has been 

 observed, and the deficiency traced to an inability to utilize nitrate nitro- 

 gen. Wlien gro\vn upon substrata containing amino nitrogen this culture 

 developed in a manner typical of P. citrinum. It was found to produce 

 citrinin when tested in bacterial spectrum plates. The culture is main- 

 tained as NRRL 2148. 



Penicillium steckii Zaleski, in Bui. Acad. Polonaise Sci.: Math, et Nat. 

 Ser. B, pp. 469-471; Taf. 50. 1927. Thom, The Penicillia, 



pp. 255-256. 1930. 



Colonies on Czapek's solution agar growing rather restrictedly, attaining 

 a diameter of about 2.0 cm. in 10 to 12 days at room temperature, consisting 

 of a close-textured, tough basal felt tearing irregularly, with surface velvety 

 or delicately fibrous, plane or irregularly wrinkled or developing shallow 

 radial furrows in marginal areas (fig. 93A), often more or less zonate with 

 growing margin 1 to 2 mm. wide, thin, white, shading quickly to dull yel- 

 low-greens with the development of conidial structures, colonies medium to 

 heavy sporing throughout, approximately gnaphalium green to pea green 

 (Ridgway, PI. XLVII) or, in age, approaching storm gray (R., PI. LII), 

 commonly developing limited, more or less flocculent and often sterile, 

 overgrowths in age and shoAving a marked tendency to develop sectors 

 differing in depth, texture, amount of sporulation; exudate limited to abun- 

 dant, mostly in small drops, from colorless to very light yellow; odor at first 

 lacking or not pronounced, in age becoming somewhat moldy or sourish; 

 reverse at first colorless or nearly so, often becoming dull yellowish near 

 olive buff (R., PI. XL) within 2 to 3 weeks; conidiophores abundantly pro- 

 duced, arising from the substratum or the basal felt (fig. 93C), variable in 

 length but usually comparatively short, rarely exceeding 200 to 250^, com- 

 monly less, by 2.8 to 3.3m, with walls smooth, usually unbranched; penicilli 

 typically biverticillate and consisting of a terminal verticil of 3 to 5 metulae 

 bearing compact clusters of sterigmata (fig. 93D) and well-defined diver- 

 gent columns of conidia up to 150m or more in length by 10 to 20m wide, 

 metulae commonly differing in length, mostly 12 to 15m by 2.8 to 3.0m but 

 ranging from 10 to 18m long; sterigmata in crowded compact clusters, paral- 

 lel, up to 8 or 10 or more in the verticil, mostly 8 to 10m by 1.8 to 2.2m, uni- 

 form in diameter except for short, somewhat narrowed conidium bearing 

 tips; conidia globose to subglobose, small, about 2.0 to 2.5m in diameter, 

 with walls smooth or delicately roughened. 



Colonies on steep agar growing somewhat more rapidly than on Czapek, 



