454 A MANUAL OF THE PENICILLIA 



cultures becoming thin and almost velvetj^; heavily sporing throughout, 

 with conidial structures arising from the substratum and from trailing 

 hyphae or ropes of hyphae; in blue-green shades approximating artemisia 

 green in young conidial areas to sage green and finally slate-olive in age 

 (Ridgway, PI. XLVII); exudate lacking or limited; odor sometimes pro- 

 nounced, mold}^ slightly fragrant; reverse colorless to drab shades; peni- 

 cilli abundantly produced, comparatively large, appressed, measuring 

 about 25 to 35yu in length but occasionally up to 50/z, consisting of the main 

 axis and usually one branch, each bearing metulae and sterigmata, with 

 conidial chains forming a loose tangled mass; conidiophores variable in 

 length, up to 300 to 400)u by about 3.0 to 3.5/x when arising from the sub- 

 stratum, or shorter, commonly 100 to 200/i in length when borne on aerial 

 hyphae, with walls smooth or very finely roughened; branches usually 10 

 to 20/i by 2.5 to 3.0^; metulae mostly in groups of 2 to 4, 10 to 15;u by 2.5 

 to 3.0m; sterigmata variable, commonly in groups of 5 to 10, 8 to 12/i 

 by 2.0 to 2.5/x, not infrequently larger, commonly borne at different levels 

 in the penicillus; conidia at first strongly elliptical, usually remaining so; 

 about 3.5 to 4.5m by 3.0 to 3.5/i, less commonly subglobose, varying greatly 

 in the same mount, with individual spores up to 5.5^ in length, walls 

 smooth, dark green in mass. 



Colonies on steep agar essentially duplicating those on Czapek's solution 

 agar, slightly deeper and with surface growth more conspicuously funicu- 

 lose (fig. IITF); penicilli as described above. 



Colonies on malt extract agar about 4.0 to 5.0 cm. in 12 to 14 days, up 

 to 500^1 deep, heavily sporing, with surface characterized by a loose net- 

 work of trailing hyphae and ropes of hyphae ; penicilli as on the above sub- 

 strata. 



Species description based upon NRRL 937 (Thom's No. 2546), received 

 from Westling and presumably type; duplicated by numerous strains iso- 

 lated from various substrata, particularly soil. 



In its cultural appearance Penicillium solitmn bears a certain resem- 

 blance to members of the P. cijclopium series. Unlike the latter forms, 

 which usually show definite fasciculation, strains of P. solitmn are generally 

 conspicuously funiculose, but occasionally show evidence of true fascicles. 

 Older colonies are commonly characterized by the development of limited 

 flocculent, white, sterile overgrowths — a phenomenon which is not un- 

 commonly encountered in P. cydopiimi. It is probable that the tw^o species 

 are more closely related than their placement in separate groups would 

 indicate. In describing P. solitum, Westling suggested comparison with 

 P. puheruhim Bainier. During our current study it has seemed increas- 

 ingly probable that these species are in fact fairly closely related and that 

 both should be considered as approaching P. cydopium Westling. It seems 



