VARIATION 75 



new. Galloway (1933) obtained marked variation in colonies of Asper- 

 gillus terreus by growing them upon media containing flour to which was 

 added 0.003 to 0.005 per cent of salicylanilide. 



Thorn and Steinberg (1939), and Steinberg and Thorn (1940a, 1940b) 

 in a series of experiments, applied chemical stimulants to a strain of A. 

 niger (Thorn No. 4247: NRRL No. 334) which had been in the collection 

 many years without noticeable change. From the cultures resulting, 

 Steinberg picked out and purified for study all variants he could observe 

 with the naked eye and with the aid of a handlens. In examining a 

 fruiting area of a colony, general changes were not common; ordinarily an 

 occasional head changed color, long or short conidiophores appeared in 

 spots, gross malformation showed as areas of no fruit, or too much fruit, 

 or color effects in the mycelium. These were picked out and grown in 

 successive cultures. Expressed in terms of morphology, the most striking 

 feature of the tested culture was disturbance of uniformity. The same 

 types of changed aspect were reproduced many times. In general, they 

 followed the same lines as have been described as present in the natural 

 series selected by Biourge or in the collections of Mosseray at Brussels. 

 In general, these changes were destructive in character and included large 

 numbers of "injury mutants", or variants, which reverted in subsequent 

 transfer to the original aspect of Steinberg's culture. Sodium nitrite was 

 the most effective agent used. Some isolations, however, represented clean- 

 cut mutations. Strains of A. fumigatus with albino heads were obtained. 

 Forms of A. niger with light brown to cinnamon-colored spore heads, es- 

 sentially like those earlier obtained by Schiemann (1912), those obtained 

 by Whelden (1940), and those subsequently obtained by Raper, Coghill, 

 and Hollaender (see below) from members of the same group, were likewise 

 isolated. These have remained stable in culture for the four years that 

 they have been in our collection. 



Whelden (1940) succeeded in obtaining a series of mutants in A. niger 

 by bombarding conidia with low voltage cathode rays and subsequently 

 isolating colonies which developed from such irradiated cells. Forms pos- 

 sessing heads in various brown shades, rather than black, were isolated, 

 as well as one giant form with conidial structures appreciably larger than 

 the parent. By means of ultra-violet irradiation of spores, Raper, Coghill, 

 and Hollaender (in press) obtained mutants which produced tan-colored 

 conidial heads but otherwise closely resembled the parent strain. In a 

 more exhaustive study of A. terreus (PI. II, A), the same investigators suc- 

 ceeded in isolating a number of striking and markedly different mutations. 

 These included albino forms with colorless conidial heads (PI. II, B); forms 

 with pale buff-colored heads; yellow, yellow-white, floccose forms with few 

 and smaller conidial heads (PI. II, C); forms producing very thin, sparsely 



