ASYMMETRTCA-VELTTTINA 377 



Series Key 



b. Colonies not producing yellow pigment in exudate or colony reverse; conidia com- 

 monly 5.0/x or more in long axis, strongly elliptical. 

 1'. Conidia elliptical, fairly uniform in size; common in soil ... .P. oxalicum series 

 aa. Colonies plane or nearly so, conidia often forming deep crusts, conidial 

 chains appearing "silky" when viewed under low power. 



P. oxalicum Currie and Thom 

 bb. Colonies radially furrowed, not forming crusts, reverse in maroon shades. 



P. atramentosum Thom 



The series is recognized as probably artificial in character and is intro- 

 duced largely as a matter of convenience to include two well-marked, 

 velvety species with elliptical, smooth-walled conidia. 



One of these species, Penidllium oxalicum Currie and Thom is especially 

 common m soil and upon various organic materials undergoing slow de- 

 terioration or decay. It is world-wide in distribution and is undoubtedly 

 one of the most ubiquitous of all the Penicillia. The species has long been 

 known to represent a normal component of the mycoflora of soils generally, 

 and it has been repeatedly encountered among the cultures isolated from 

 tentage and other military equipment subjected to field conditions. As 

 the name implies, typical strains produce some oxalic acid, although the 

 amount produced is generally much less than that from selected cultures 

 of Aspergillus niger. The species is marked particularly by its very abun- 

 dant spore production in newly isolated strains. In their typical aspect, 

 these are uniformly and deeply velvety and not infrequently develop con- 

 tinuous layers of spores from 0.5 to 1.0 mm. deep over the entire colony area 

 (figs. lOOA and B). Viewed with a hand lens, the colony surface commonly 

 has a silky appearance. When the culture dish or tube is lightly tapped 

 the conidia are loosened and break away as shown in figs. lOOC and D ; or 

 when sharply struck they produce a dense cloud quickly filling the culture 

 vessel. The species is further distinguished by its large, strongly elliptical, 

 smooth-walled conidia. These originate as cylindrical cells hardly dis- 

 tinguishable from the terminal areas of the parent sterigmata, but as they 

 mature they gradually assume their characteristic elliptical form. 



The second species, Penidllium atramentosum Thom is doubtfully closely 

 related to P. oxalicum. Yet the two species possess sufficient characters 

 in common to enable the mycologist to locate the species here more readily 

 than anywhere else. Colonies of P. atramentosum on Czapek are usually 

 azonate, radially furrowed and strictly velvety (fig. 101 A); penicilli are 

 usually biverticillate and asjonmetrical, smooth-walled throughout, and 

 bear smooth-walled elliptical conidia. Unlike P. oxalicum, which is un- 

 usually common and widely distributed, P. atramentosum appears to be 

 comparatively rare. Of three numbered strains available for the present 

 study, two are known to have stemmed from the type culture w^hich was 



