Chapter XXI 

 THE ASPERGILLUS OCHRACEUS GROUP 



Outstanding Characters 



Conidial heads ranging from sulphur yellow to varying shades of ochra- 

 ceous, depending upon the species and strain, showing a greenish tint 

 only in the single species A. sparsus; heads globose or radiate with 

 conidial chains commonly adhering into divergent columns. 



Conidiophores normally showing shades of yellow in the outer layers of 

 the wall which is rough or pitted, usually prominently but occasionally 

 reduced to traces which are seen most readily in dry mounts. 



Sterigmata in two series with the primary often quite large and septate. 



Conidia in some series thin -walled and smooth, in others showing defi- 

 nitely double walls, more or less roughened or echinulate. 



Sclerotia present in most species and strains, often dominating the cul- 

 tures; in others entirely lacking. When present, ranging in color from 

 cream or buff through pink and orange shades to purplish-vinaceous. 



Molds belonging to this group are common wherever organic matter is 

 decomposing under natural conditions. In spite of great variation in super- 

 ficial appearance, length of conidiophore, size of heads, intensity and shades 

 of color, and sclerotium production, they fit together into a great natural 

 group of related forms. Extreme variants in the several series can be easily 

 considered separate species and have been so described, but collections of 

 great numbers of such forms present so many gradations that identification 

 by description becomes doubtful if not impossible. Allocation to series 

 centered upon some described species gives a practical method of grouping 

 together closely related members of the great aggregate. 



The name "ochraceus", derived from the pigment ocher and attached to 

 the most abundant series in the group, is an old mycological usage which was 

 more or less definitely followed in Saccardo's use of it for a plaque in his 

 Chromotaxia. Ridgway analyzed the colors more exactly, dropped the 

 term ochraceus but included a plaque near to it as PI. XV, Col. 15 YO, 

 Ochraceous-Buff . The strains of this group, however, mostly show colors 

 closer to the yellower tints in Ridgway's Plate XXX, column 19. It is im- 

 portant that relationship with the great group shall be quickly grasped 

 whether exact identity with particular strains already known is claimed or 

 not. 



Group characterization : The colony appearance of this group of Asper- 

 gilli varies greatly with the presence or absence of sclerotia. Some species 



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