338 A MANUAL OF THE PENICILLIA 



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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 378 



bb. Colonies radially furrowed, not forming deep crusts, reverse 



in maroon shades P. atramentosum Thom 381 



2'. Conidia strongly elliptical to cylindrical, varying greatly in size I 

 and often very large; penicilli very irregular, often fragmen- 

 tary; produces "green" citrus rot P. digitatum series 385 



P. digitatum Sacc. 386 

 aa. Conidia white; otherwise duplicating the species. 



P. digitatum Sacc. var. californicum Thom 390 

 2. Conidiophores typically rough-walled; colony margins usually appear- 

 ing arachnoid P. roqueforti series 392 



a. Colonies broadly spreading, with surface plane or nearly so ; margins 



thin, appearing arachnoid P. roqueforti Thom 395 



b. Colonies restricted, strongly wrinkled or furrowed, margins hardly 



arachnoid P. casei Staub 401 



B. Penicilli comparatively short, compact, with all elements closely ap- 



pressed P. hrevi-compactum series 40-4 



1. Penicillus typically showing one or more side branches below the level 



of metulae. 



a. Conidiophores coarse, with branches and metulae commonly in- 



flated P. hrevi-compactum Dierckx 407 



b. Conidiophores thinner, fle.xuous, with branches and metulae not 



inflated P. stoloniferum Thom 412 



2. Penicillus typically consisting of a single, crowded, terminal verticil 



of 5 to 8 metulae P. paxilli Bainier 414 



Penicillium citrintjm Series 

 Outstanding Characters 



Colonies growing rather restrictedly on Czapek's agar, typically thin but 

 varying in depth and general texture depending upon the species and 

 strain, fruiting surface appearing velvety, usually medium to heavy 

 sporing, in bluish green to yellowish green shades, often producing abun- 

 dant exudate ranging from colorless to bright yellow; reverse usually in 

 yellow, dull orange or light browTiish shades, in one species becoming 

 almost black. 



Conidiophores erect, comparatively short, mostly less than 200)u in length, 

 arising as a dense stand from the substratum or the basal felt, less com- 

 monly from aerial hyphae in more floccose strains, smooth-walled, usually 

 unbranched except in the terminal area. 



Penicilli typically consisting of a terminal cluster of 3, 4, 5, or occasionally 

 more metulae, each bearing a crowded cluster of parallel sterigmata and 

 chains of conidia commonly (but not consistently) adherent in well- 

 defined and rather divergent columns. The penicillus commonly 



