ASYMMETRiCA-VELUTiNA 347 



the agar becoming similarly colored and often assuming a definite pinkish 

 tint; conidiophores arising mostly from the substratum, or from aerial 

 hyphae in the deeper colony centers or in floccose strains, mostly 50 to 200/i 

 in length by 2.2 to 3.0m in diameter, usually unbranched but occasionally 

 bearing one or more branches 25 to 35ju in length, smooth -walled through- 

 out; penicilli typically consisting of a terminal group of 3, 4, or occasionally 

 more, somewhat divergent metulae (fig. 9OB2) that measure about 12 to 

 20/i by 2.2 to 3.0m (apices commonly enlarged to 4.0 or 5.0m), each support- 

 ing a cluster of 6 to 10, more or less crowded and parallel sterigmata measur- 

 ing about 8.0 to 11.0m by 2.0 to 2.8m, and bearing conidia in parallel chains 

 to produce well-defined columns up to 100 to 150m in length (fig. 90Bi); 

 conidia globose to subglobose, mostly 2.5 to 3.0m but ranging from 2.2 to 

 3.2m, smooth-walled or nearly so, but often appearing granular when ex- 

 amined in air bubbles. 



Colonies on steep agar growing more rapidly, attaining a diameter of 

 2.5 to 3.0 cm. in 10 to 12 days at room temperature, heavier sporing and 

 more closely furrowed, but in general exhibiting the same basic features 

 as on Czapek; exudate limited to abundant, pale yellow; reverse in yellow 

 to light bro^vn shades; penicilli as described above. 



Colonies upon malt extract agar restricted (fig. 92B), rarely exceeding 

 2.0 cm. in diameter at 10 to 12 days, plane, velvety, heavy sporing through- 

 out, near grayish blue-green (R., PI. XLVIII), with conidiophores arising 

 from the substratum in a dense stand; no exudate produced; reverse dull 

 yellow to orange. The restricted growth of the species upon this substrate 

 is fairly distinctive and is in marked contrast to the behavior of most Peni- 

 cillia which produce thin spreading colonies when gro^\^l upon malt extract 

 or wort agars. 



Species diagnosis based upon the examination of many different strains, 

 of which the following are representative: NRRL 805, isolated in 1940 in 

 Washington as a laboratory contaminant; NRRL 806 (fig. 92A and B), 

 received in 1932 from Professor G. Sabut, Egyptian University, Cairo, 

 Egypt; and NRRL 1842 (fig. 92C and D), received in 1942 from George 

 Smith, London School of Hygiene and Tropical Medicine, as their No. P25. 



Our concept of Penicillium citrinum Thom is broad in scope and includes 

 forms which vary substantially in particular characteristics, yet possess 

 certain basic features in common. Unquestionably they are inter-related 

 and so belong together. While no exact tabulation has been attempted, it 

 is safe to say that more than 75 per cent of the strains that produce some 

 citrinin and possess penicilli of the citrinum-type comply fully with the 

 species description. The remaining related strains can be grouped as 

 follows : 



(1) Forms which grow more rapidly and are heavier sporing: Colonies 



