236 A MANUAL OF THE ASPERGILLI 



alone, the subject is covered in the chapters on Morphology and on Varia- 

 tion. 



Coloration 



Color has been emphasized in most of our attempts to separate these 

 strains in culture. Linossier (1891) extracted from his strain of A. niger 

 a coloring substance soluble in hot water which he called aspergilline. 

 This substance is readily demonstrated. Blochwitz (1929, p. 219) reports 

 this material to be soluble in "NH 3 and alkalies," and we have extracted it 

 with hot water. Microscopic comparison of conidiophores, heads, and 

 separate conidia from numerous strains leads to the conclusion that the 

 same substance may give a brown color to the upper one-third of the 

 conidiophore, to the vesicle and its contents, to the walls of the sterigmata, 

 and in A. carbonarius so fill the whole vesicle and sterigmatic area with a 

 brittle mass as to justify Bainier in calling the head carbonaceous. Conidia 

 in a few strains have appeared to possess smooth, uniformly brown cell 

 walls. As a group, however, the black aspergilli have globose conidia with 

 a firm, uncolored or slightly colored inner wall, a very thin outer wall, and 

 between the two the coloring substance, presumably aspergilline, deposited 

 as granules, warts, or bars running lengthwise of the cells and presenting 

 a pattern characteristic of the whole group. When pale-colored variants 

 (mutants?) such as A. cinnamomeus (p. 223), or darker ones such as A. 

 schiemanni (p. 224), or the variously brown to deep carbon black ones 

 like A. carbonarius are compared, the relative quantities of coloring matter 

 seem to account for the progressive darkening of the head colors as de- 

 scribed in the series. 



In the "reverse", or underside, of the mycelium and in the culture 

 substratum, a range of shades from colorless to yellows to reddish-brown, 

 and even very dark shades, is reported for particular species growing upon 

 specified substrata. The chemical reactions back of these colors are not 

 known for the black aspergilli. Blochwitz has reported extractions of 

 color from various species of Aspergillus and other molds, and observed 

 that variations in these colors were readily obtained with reagents. Some 

 of the extracted materials were reported to act as indicators. It is, there- 

 fore, doubtful whether the succession of colors present in such a related 

 series of organisms represent substances differing .fundamentally one from 

 another, or merely successive steps in the transformation and reactions of 

 the same general type of product. 



Occurrence and Economic Importance 



The black aspergilli are probably more common than any other repre- 

 sentatives of the genus. They are world-wide in distribution and occur 



