74 A MANUAL OF THE ASPERGILLI 



The same mitosis occurs. One active and one resting nucleus result, but 

 the resting nucleus remains in the sterigma while the active nucleus moves 

 into the newly forming cell. This determines the course of development. 

 The active, multiplying nucleus is always in the newest cell formed. 



Previously Barnes (1928) had stimulated a strain of the A. glaucus group 

 (identified by us as A. amstelodami, 1941) by heat, and reported certain 

 mutants which were deposited with Dr. Westerdijk at Baarn. Among 

 them, under the designation "Creamy" (NRRL No. 143), a mold with the 

 morphology of Cladosarum appeared. It was obviously derived from 

 some A. glaucus strain and is, in so far as the writers are aware, the only 

 other appearance of the Cladosarum structure ever discovered. Barnes 

 does not appear to have recognized its contrasting structure. 



Since no collector has reported this type of mutant in nature, it must 

 either be very rare or be unable to maintain itself in a competitive environ- 

 ment. However readily such mutants may be maintained in the labora- 

 tory, they would rarely reach the second generation in nature on account 

 of lack of spores. The name Cladosarum was thus applied to a defective 

 organism (zoologically designated a "monster"), which does not become a 

 component of any natural flora, hence taxonomically the name should 

 be untenable. 



INDUCED VARIATION 



Striking mutations have been obtained from various species of the Asper- 

 gilli by subjecting them to artificially imposed stimuli. Schiemann (1912) 

 was among the first to draw attention to the possibilities inherent in this 

 approach. By subjecting a strain of A. niger to various concentrations of 

 potassium bichromate, she was able to produce two striking mutations 

 which she designated according to color, A. fuscus (= A. niger mut. schie- 

 manni of this manual) and A. cinnamomeus (= A. niger mut. cinnamomeus 

 ibid.), respectively. Both cultures have remained stable in our hands, and 

 in various collections, throughout the 32 years since their original isolation. 

 A third "mutation" designated A. niger var. altipes could not be 

 distinguished from other strains of black Aspergilli isolated from nature — 

 the parent strain was not seen. Working with a member of the A. glaucus 

 group designated Eurotium herbariorum Wigg., Barnes in 1928 reported 

 the production of a series of variations by exposing spores to heat. While 

 there are reasons for questioning the correctness of some of Barnes' inter- 

 pretations and conclusions (see Thorn and Raper, 1941), there is evidence 

 that he succeeded in producing a mutant which, in its habit of growth and 

 in the character of the fruiting structures developed, bears a striking re- 

 semblance to a form subsequently isolated from A. niger by the Yuills 

 (1938), and described by them as Cladosarum olivaceum, genus and species 



