632 A MANUAL OF THE PENICILLIA 



Members of the series represent normal constituents of the mycoflora 

 of all soils examined, and may occur also upon a wide variety of organic 

 substrata undergoing slow decomposition. 



Several species, apparently belonging to this series, have been described 

 and it is extremely difficult to know which of these should be accepted as 

 valid, and which should be reduced to synonymy. Our selection of species 

 for recognition is admittedly somewhat arbitrary, as it is in the other major 

 series which comprise this section of the genus, and further studies may 

 indicate a need for revision or emendation of the scheme here proposed. 

 Based upon re-examination of original descriptions and an extensive study 

 and comparison of cultural material, we believe that a separation similar 

 to that proposed will prove adequate for most investigators. Four species 

 are recognized: 



Penicillium purpurogenum Stoll is the most abundant and the most 

 variable. Typically, it is characterized by dark yellow-green conidial 

 masses against a mycelium and substrate colored in red or purple-red 

 shades. Spores are strongly elliptical and more or less roughened in most 

 strains. On malt agar, colonies commonly produce an aromatic or fragrant 

 odor suggesting apples or black walnuts. 



Penicillium rubrimi Stoll differs from the above in producing more re- 

 stricted colonies upon most substrata and in producing conidial areas of 

 lighter yellow to gray-green color. Pigmentation of the colonies and the 

 underlying medium is essentially as in P. purpurogenum. The conidia 

 of this species are smooth-walled and often subglobose. 



Pmicilliuni aculeatum Raper and Fennell is characterized by very re- 

 stricted and comparatively deep colonies on Czapek agar. Penicilli are 

 relatively shorter and broader than in the preceding species and conidia 

 are strictly globose and strongly echinulate. 



Penicillium variabile Sopp is characterized by a marked reduction in red 

 pigmentation, but retains the other cultural characteristics of the series. 

 In many strains there is an excessive development of sterile yellow mycelium 

 which oftentimes dominates the colony appearance. Conidia are strongly 

 elliptical and smooth-walled. The colony reverse usually shows yellow- 

 orange to orange-brown, rather than true red shades. 



Thom, in his Monograph 1930, recognized a series of strains under the 

 name "Penicillium luteum series— non-ascosporic," to which he assigned 

 forms that showed a strong admixture of yellow-encrusted aerial hyphae 

 and dark yellow-green conidial heads, often with colonies somewhat red in 

 reverse. It was his belief that these forms, in the main, probably repre- 

 sented haplonts of fertile forms which, for one reason or another, had be- 

 come segregated and hence incapable of developing their complete hfe 

 cycle. Gradually our interpretation of the series was broadened until it 



