MORPHOLOGY AND DESCRIPTION 13 



concentric zones and result from an increased production of conidial 

 structures periodically during the development of the colony (fig. 1 F). 

 The exact conditions and factors responsible for their appearance has not 

 been determined, but they obviously develop, in some way, as a response 

 of the fungus to its environment. Particular strains cannot generally be 

 described as either zonate or azonate, since the same organism exhibits 

 both characters at different times and under different conditions. In 

 contrast to concentric zones, certain species in laboratory culture char- 

 acteristically develop conidial heads in localized areas only. This is 

 particularly true of members of the A. glaucus group, and the A. sulphur eus 

 series, with conidial heads normally more concentrated at the margins of 

 slant tube cultures. 



Coremia, in the broader sense of ropes of hyphae anastomosing and 

 trailing upon or near the surface of a substratum, occur more or less 

 commonly in Aspergilli of certain groups; but as specialized erect aggrega- 

 tions of conidiophores (StilbumAike) , such structures are described and 

 figured only for A. vitelline/, of Ridley. Since Ridley apparently de- 

 scribed his form only as collected upon a natural substratum, the actual 

 development of a specialized structure in this form remains doubtful. 

 Ridley's figure could be repeated many times by roughly drawing masses 

 of conidiophores bursting through the otherwise unbroken surface of a 

 rich nutrient substratum, such as seeds of cereals, producing a dense 

 cluster of conidiophores. 



COLOR 



The most striking character of an Aspergillus colony is usually its color 

 production. This takes two general forms: (1) color in the aerial parts, 

 including hyphae, conidiophores, heads, and conidia; (2) colors appearing 

 in the substratum, and representing the specific response and effect of the 

 organism upon particular media. The former is universally used in the 

 characterization of species, while the latter usually furnishes additional 

 pertinent data. In our study of the Aspergilli, citations of color have been 

 made according to the terminology employed by Ridgway since the 

 publication of his "Color Standard and Nomenclature" in 1912. This 

 terminology is used consistently in the present manual. 



Group Color 



There is a characteristic range of colors for each group (or collective 

 species) of Aspergilli, with a much narrower range in successive cultures 

 of the particular species or strains. The coloring substance may be de- 

 posited in the conidia only, as in A.flavus; in the conidial wall, and more or 

 less present in the sterigmata, vesicle, and upper part of the conidiophore 



