ASYMMETRICA-VELUTINA 339 



presents the aspect of a cluster of monoverticillate fruits when viewed 

 under low magnifications. 



Conidia comparatively small, mostly 2.5 to 3.2/i, globose to elliptical de- 

 pending upon the species and strain, with walls smooth or delicately 

 roughened. 



Production of the antibiotic citrinin is characteristic of the principal species. 



Series Key 

 (See General Kej^ to Velutina) 



IMembers of the series are very abundant and widely distributed in 

 nature. They are encountered among the isolates from almost all soils 

 examined, and have occurred with greater frequency than any other series 

 of Penicillia among the isolates from deteriorating military equipment 

 submitted to us for identification. They appear to be particularly abun- 

 dant in tropical and sub-tropical areas. 



Colonies of different species and strains vary appreciably in texture, 

 color, and the abundance of fruiting structures when gro^^^l upon Czapek's 

 solution agar. They are generally rather restricted, more or less radially 

 wrinkled, and are characterized by the presence of varying amounts of exu- 

 date ranging from colorless to bright yellow. Upon malt extract agar, 

 colonies vary greatly depending upon the species, with this character pro- 

 viding a useful and generally reliable key to species identity: in Penicillium 

 citrinum Thorn, colonies are consistently restricted and are generally 

 smaller than on Czapek, plane, heavy sporing, commonly up to 300^ or 

 more deep, and with reverse typically in orange-yellow shades. In P. cor- 

 ylophilum Dierckx, on the other hand, colonies are broadly spreading, 

 thinner, with reverse in light bro^^^l to dark shades approaching black in 

 localized areas or sectors. In P. steckii Zaleski, colonies tend to be inter- 

 mediate between the above both in rate of growth and in general colony 

 texture. 



The outstanding diagnostic feature of the series lies in the distinctive 

 character of the penicilli. Typically, these consist of terminal clusters of 

 metulae arising from unbranched conidiophores. The metulae tend to 

 diverge. Sterigmata vary in number but generally range from 5 to 10 per 

 metula, are comparatively short, and bear conidia from apices which are 

 not conspicuously pointed. The sterigmata are generally crowded and 

 essentially parallel and in most forms tend to bear conidial chains in com- 

 pact columns which superficially suggest separate, monoverticillate peni- 

 cilli. 



Three species are recognized, namely: Penicillium citrinum Thorn, P. 

 steckii Zaleski, and P. corylophilum Dierckx. 



Penicillium, citrinum is by far the most abundant and the most variable, 



