378 A MANUAL OF THE PENICILLIA 



isolated by Thom more than forty years ago. Some additional strains 

 have been examined in the intervening years, but the number has been 

 limited. Although the type was isolated from cheese, it is probably safe 

 to regard the species as typically a soil fungus. 



Penicillium oxalicum Currie and Thom, in Jour. Biol. Chem. 22: 289, fig. 1. 

 1915; also Thom, The Penicillia, pp. 247-248, fig. 31. 1930 



Colonies upon Czapek's solution agar broadly spreading, attaining a 

 diameter of 3.5 to 5.0 cm. in about 10 days at room temperature, generally 

 plane (fig. lOOA) but in some strains irregularly furrowed (fig. lOOF), 

 strictly velvety in typical strains including most new isolates, heavily spor- 

 ing with conidia forming a deep layer which, when mature, characteristically 

 falls away en masse if the culture vessel is tapped (fig. lOOC and D), shading 

 from pale blue-green in young spore areas to dull green shades near sage 

 green (Ridgway, PI. XLVII) or blue-green shades near Russian green (R., 

 PL XLII) in colony centers, becoming slate olive to deep slate-olive (R., 

 PI. XLVII) or storm to castor gray (R., PL LII) in age, vegetative my- 

 celium largely submerged, often extending 2 mm. or more beyond the 

 limits of conidium production, growing marginal zone 1 to 2 mm. wide, 

 white or nearly so, becoming blue-green with the development of conidia; 

 generally producing no exudate; no odor; colony reverse uncolored in some 

 strains but generally in yellowish, orange, or more commonly pink shades; 

 penicilli typically biverticillate and asymmetric (fig. 99A), produced in 

 great abundance, borne upon smooth-walled conidiophores 100 to 200/x by 

 3.5 to 4.5m arising from the substratum in a close stand to produce a velvety 

 colony surface, occasionally monoverticillate but normally biverticillate 

 with 2 or 3 metulae, or metulae and branches arising from the same level, 

 with all cellular elements appressed and with conidial chains forming col- 

 umns up to 500/i or more in length by 10 to 15^ in diameter, appearing silky 

 when viewed under very low magnifications, becoming entangled with 

 similar columns from adjacent penicilli to form a deep spore layer which 

 breaks off in the manner noted above ; branches absent or borne singly, 10 to 

 20ju by 3.5 to 4.5/x, often arising from the same level as one or more metulae; 

 metulae usually in groups of 2 or 3, rarely more, 15 to 20m by 3.3 to 3.8m; 

 sterigmata borne in terminal clusters of 6 to 10, rarely more, 9.0 to 15.0m 

 by 3.0 to 3.5m, with conidium-bearing tips more or less tapered; conidia 

 persistently elliptical (fig. 99A2), smooth-walled, ranging from 4.5 to 6.5m 

 by 3.0 to 4.0m, but mostly 5.0 to 5.5m by 3.0 to 3.5m. 



Colonies upon steep agar, and to a less extent upon malt agar, grow more 

 rapidly (fig. lOOB), tend to be less deeply furrowed, and are generally 

 heavier sporing than upon Czapek agar, producing heavy layers of conidia 



