182 A MANUAL OF THE PENICILLIA 



Colonies on malt extract agar growing even more rapidly than on steep 

 agar, plane, but usually showing a loose flocculent felt 2 to 3 mm. deep, 

 heavily sporing throughout; drops numerous, enmeshed in the felt; peni- 

 cilh as above but with chains of conidia showing a greater tendency to 

 form columns. 



Species description based upon Thom's notes on the type strain, his 

 No. 45, isolated as a contaminant from a culture of another Penicillium 

 obtained from Dr. Wehmer's Laboratory in Hanover, Germany, and upon 

 observations made since that time and in the current study on a large 

 number of strains having essentially the same cultural and morphological 

 characteristics. NRRL 1750 may be regarded as representative. This 

 culture stems from a transplant of Thom's No. 45 made in 1930 by Dr. 

 H. C. Greene and subsequently maintained at the University of Wis- 

 consin, Madison, until the spring of 1941 when it was returned to us for 

 the NRRL Collection. Thom's type, as maintained in his collection in 

 Washington, D. C. until 1940, and subsequently at the Northern Regional 

 Research Laboratory in Peoria, no longer represents the species adequately. 

 It is now essentially floccose and almost non-sporulating but still produces 

 penicilli (usually small) and conidia characteristic of Penicillium spinulo- 

 sum. This tendency toward sterility in strains long maintained in arti- 

 ficial culture is frequently encountered in this and certain other species, 

 e.g. P. oxalicum and P. purpurogenum. The following may be listed as 

 additional representative strains: NRRL 724 received in 1940 from Pro- 

 fessor E. M. Gilbert, University of Wisconsin; NRRL 728 from Biourge 

 as his P. roseo-maculatum (Thom No. 4733.107); and, NRRL 2051, a 

 strain received in February 1946, from the Centraalbureau as Biourge 's 

 culture of his P. flavo-cinereum. 



Penicillium spinulosum is world-wide in distribution and is especially 

 common in soil, as evidenced by its frequent isolation from this source. 

 Although confirmation has not been possible, there appears to be some 

 evidence that this species is near, if not identical with, Citromyces pfefferi- 

 anus Wehmer (Beitr. Kennt. Einh. Pilze I: 22-24; Taf. I, figs. 1-13. 

 1893). 



Within the species Penicillium spinulosum, individual strains vary 

 appreciably in cultural characteristics, particularly with reference to depth, 

 general colony texture, and amount of sporulation. Strains also differ 

 in the ,degree of roughness shown by conidia and conidiophores. A few 

 strains produce conidia more or less elliptical in contrast to the usual 

 and more typical forms with conidia globose or subglobose. 



Representative strains of Penicillium frequentans Westhng and P. 

 spinulosum Thom are fairly distinct, and these can usually be identified 

 or separated without serious difficulty. Nevertheless, strains of some- 



