ASTMMETRICA-VELUTINA 355 



PeNICILLIUM CHRYSOGENTJIM SeRIES 



Outstanding Characters 



Colonies tjTDically velvety, ranging from close to loose-textured in appear- 

 ance, with conidiophores usually arising in a dense stand from the sub- 

 stratum or a basal felt; in some strains more or less floecose, with co- 

 nidiophores borne as branches from aerial hyphae ; usually characterized 

 by conspicuous furrows forming a radiate or wheel-like pattern. 



Colonies generally characterized by abundant exudate, often collecting into 

 conspicuous droplets, ranging in color from light to rich yellow. 



Colony reverse usually in shades of yellow, commonly becoming brown in 

 age, with surrounding agar usually yellow in color, often conspicuously so. 



Penicillus asymmetrical, smooth-walled throughout, irregularly branched 

 in larger structures, or commonly consisting of a terminal verticil of 

 metulae in smaller fruits; often characterized by well-defined columns of 

 conidia that arise from individual verticUs of sterigmata, which when 

 viewed separately appear almost as monoverticillate structures. 



Conidia smooth-walled, varying from globose to subglobose in some forms 

 to definitely elliptical in others, and ranging in size from approximately 

 2.5 to^4.0M or 4.5^ in_diameter. 



Series Key 



1'. Conidia elliptical, or occasionally subglobose. 



aa. Colonies usually showing abundant yellow exudate and yellow pigmenta- 

 tion in reverse P. chrysogenum Thom 



bb. Colonies showing pale or colorless exudate, and vinaceous to brownish 



fawn colors in reverse P. meleagrinum Biourge 



2'. Conidia globose to subglobose. 



aa. Colonies velvety, heavily sporing, in rich blue-green shades, often com- 

 paratively thin P. notatum Westling 



bb. Colonies loose-textured, flocculent, often lightly sporing, comparatively 

 deep P. cyaneo-fulvum Biourge 



The members of this series are especially common in nature and regularly 

 occur in soil and upon a wide variety of organic substrata. They have 

 received much detailed study during the past few years because of their 

 capacity to produce the antibiotic penicillin (see Chapter V). 



Members of the series as isolated from nature are quite variable in pig- 

 mentation, exudate formation, colony texture, rate of growth, etc., yet all 

 show the general features indicated above and can be readily recognized. 



Cultures long maintained in the laboratory may remain quite stable and 

 reduplicate, year after year, their original cultural and morphological char- 

 acteristics. Or they may undergo progressive variation, and in a relatively 

 short time evolve or degenerate into flocculent and lightly sporulating forms 



