32-i A MANUAL OF THE PENICILLIA 



dark, gray or olive-brown shades — almost black on some substrata; 



reverse typically developing deep orange-red shades; with exudate in 



many forms similarly colored. 

 Conidiophores varying greatly in length and in origin, arising either as 



short branches from aerial hyphae, as ascending hyphae or as separate 



conidiophores directly from the substratum. 

 Penicilli typically strongly divaricate, consisting of divergent metulae 



arising at one or more levels and bearing clusters of sterigmata giving 



rise to loose columns or tangled masses of conidia; monoverticillate 



penicilli not uncommon. 

 Conidia globose to subglobose, strongly echinulate in some forms, with 



color apparently concentrated in bars or tubercles between the outer 



and inner spore walls, smooth or nearly so in others. 



Series Key 

 b. Ripe conidia typically in dull gray shades (scarcely showing any green) such as 

 steel gray to dark olive gray (Ridgway), globose; colony reverse usually in 



yellow to deep orange shades P. nigricans series 



1'. Conidiophore walls smooth or nearly so on all substrata, 

 aa. Conidia strongly echinulate with conspicuous color bars. 

 1". Colonies heavily sporing, dull to dark gray in color. 



P. nigricans (Bainier) Thorn 

 2". Colonies floccose, light sporing, white or nearly so. . . P. albidum Sopp 



bb. Conidia delicately echinulate P. kapuscinskii Zaleski 



2'. Conidiophore walls coarsely roughened, at least on malt agar. 



aa. Conidia conspicuously echinulate P. melinii Thom 



bb. Conidia smooth or nearly so P. raciborskii Zaleski 



Members of this series are regular components of the mycoflora of soil 

 and have been isolated from samples world-wide in origin. They seem to 

 be especiall}^ abundant in forest soils upon organic constituents in the 

 later stages of decomposition. They are occasionally isolated from other 

 substrata subject to air and dust borne contamination. In his Monograph, 

 Thom (1930) discussed these forms under the "Pemcillium nigricans- 

 janczewskii Series". Subsequent study has seemed to establish the iden- 

 tity of these two species, hence, their present consideration under the single 

 name, P. nigricans series. 



The series includes five species, as follows: Penicillium nigricans (Bainier) 

 Thom, P. kapuscinskii Zaleski, P. albidum Sopp, P. melinii Thom, and 

 P. raciborskii Zaleski. Of these species, P. nigricans is by far the most 

 abundant, and if we expand our concept of this species to accommodate 

 recurring variant types which show consistent but limited differences, the 

 species and the series become almost one and the same thing. While 

 realizing that they may represent little more than striking cultural variants 

 from P. nigricans, we believe the user of the Manual will be benefited by 



