VARIATION 73 



In studying a group of cultures three years ago, the authors noted a few 

 tan heads in the form of a Y-sector in an otherwise typical black colony of 

 A. niger (fig. 17A). Isolations from a tan head reproduced the mutant head 

 characters, and repeated transfers of this strain have proved consistently 

 stable over a period of three years. The mutant strain cannot be 

 distinguished from A. niger mut. cinnamomeus (A. cinnamomeus of Schie- 

 mann). 



In dealing with natural as well as induced mutations, we have endeavored 

 to limit the use of the term mutant to forms whose origin was definitely 

 known. Blochwitz (1934, 1935) was not so precise. Under the name 

 A. glaucus mut. alba he refers to a white-spored member of the A. glaucus 

 group. He believed Aspergillus giganteus Wehmer to represent essentially 

 a long-stalked .4. clavatus, hence designated it A. clavatus mut. giganteus. 

 This treatment may be justifiable. We believe, however, that until their 

 origin from other and well-marked species can be proved, it is wise to con- 

 tinue to recognize as species these very distinct forms that are isolated from 

 and are able to maintain themselves in nature. 



Cladosarum: The most striking variant, or mutant, ever described in the 

 Aspergilli is Cladosarum olivaceum of Yuill and Yuill (1938) . This appeared 

 in a culture of A. niger growing on bread at 28° C. (Personal correspond- 

 ence). Its colony, conidiophores, vesicles, and primary sterigmata are 

 those of Aspergillus. The secondary sterigmata, instead of producing co- 

 nidia, thrust out cells which are essentially the same in morphology as the 

 secondary sterigmata themselves; the same procedure is then repeated 

 several times. Occasionally, however, a terminal cell changes and thrusts 

 out several equal cells; in other words, it resumes the function of a primary 

 sterigma. The new secondaries repeat the process of producing chains of 

 cells each resembling the basal cell with the aspect of a sterigma not a conid- 

 ium, and always with the youngest cell at the tip of the chain. In Asper- 

 gillus the sterigma which produces a chain of conidia always produces the 

 new conidium at the base of the chain, shoving the next most recent farther 

 out. Differing then from Yuill 's interpretation, Cladosarum produces no 

 conidia, however readily any cell detached from the mass may grow. 



In Aspergillus the ordinary nuclear procedure in conidium formation 

 involves mitosis in the sterigma actually producing the conidia. After 

 each mitosis one daughter nucleus migrates through the tube into the new 

 spore in which it "rests" until that spore begins to germinate. The other 

 nucleus remains in the sterigma and repeats the process. This goes on 

 until there may be a chain of 200 conidia — the oldest at the outer end, the 

 newest directly attached to the sterigma. 



In the absence of cytological study, one may offer the following 

 hypothesis. In "Cladosarum" the nuclear procedure must be reversed. 



