BIVERTICILLATA-SYMMETRICA 647 



Conidia persistently elliptical, variable in size, with walls usually roughened 



but appearing smooth in some species and strains. 

 Odor usually lacking or indistinctive. 



Series Key 



1'. Colonies restricted, close-textured, usually strongly folded or wrinkled. 



aa. Conidia elliptical, conspicuously rugulose; penicilli typically biverticillate- 



symmetrical but often irregular in pattern P. rugulosum Thorn 



bb. Conidia strongly elliptical, smooth or slightly and irregularly roughened; 

 penicilli more consistently bivcrticillate-symmetrical. . . P. variabile Sopp 



(in the P. purpurogenurn series) 

 2'. Colonics very restricted, or very thin and plane, but with central area commonly 

 raised or floccose. 

 aa. Colonies very thin throughout or with central area somewhat floccose, grow- 

 ing more or less restrictedly upon all substrata P. tardum Thom 



bb. Colonies growing very restrictedly upon Czapek, but heavily sporing and 

 broadly spreading on media containing ammonium nitrogen. 



P. diversum Raper and Fennell 

 1". Colonies producing abundant yellow, much-branched mycelia on malt, 

 often tending to characterize the culture. 



P. diversum var. aureum Raper and Fennell 



The series includes a number of slowly growing forms which are regu- 

 larly encountered in the mycoflora of soils. They appear to be widely dis- 

 tributed and occur with considerable frequency upon decaying vegetation 

 and a variety of other organic materials subject to processes of weathering 

 and slow decomposition. They have been repeatedly encountered among 

 the Penicillia isolated from tentage and other protective fabrics in the field. 

 Two fairly- well defined subseries are recognized: 



The first of these is typified by Penicillium rugulosum Thom and is char- 

 acterized by restricted, compact colonies on Czapek's agar which usually 

 show an admixture of sterile, encrusted vegetative hyphae and dark yellow- 

 green conidial heads in greater or less abundance. Colonies on malt agar 

 are heavier sporing and usually somewhat faster growing, but remain re- 

 stricted in comparison with species such as P. funtculosum and P. purpuro- 

 genurn considered above. Penicillium rugulosum is characterized particu- 

 larly by its strongly elliptical and conspicuously rugulose conidia. 



The second subseries is typified by Penicillium tardum Thom and is 

 characterized by very thin or extremely restricted colonies on Czapek's 

 solution agar. In the species P. tardum, growth on all substrata is regu- 

 larly restricted. In some other forms, colonies on nutrient-rich media such 

 as malt agar are luxuriant, broadly spreading, and heavily sporing. Limited 

 growth on Czapek's agar can be attributed to definite nutritional deficien- 

 cies in some cases, and when these are supplied, the thin or restricted forms 

 may duplicate well-recognized species and thus be properly assigned. In 



