410 PHYSIOLOGY OF THE FUNGI 



brown color; one dominant and one recessive factor gave lighter shades 

 of brown ; while a combination of the two recessive factors gave pure white 

 mycelium. 



The normal haplont of Peniophora allescheri is reported (Nobles, 1935) 

 as slow-growing with scant mycelium bearing conidia. A mutant grew 

 rapidly with abundant mycelium but bore no conidia. The combination 

 of normal haplont and mutant haplont yielded diploid mycelium which 

 grew rapidly and abundantly and produced conidia. Thus, rapid growth 

 and conidial production were dominant over slow growth and nonproduc- 

 tion of conidia. 



Bioluminescence of the North American race of Panus stypticus was 

 found (Macrae, 1942) to be dominant over nonluminescence of the 

 European race when the two haplonts were crossed (Fig. 77). 



The single-spore isolates from a single fruit body of Lenzites trahea were 

 found (Lilly and Barnett, 1948) to vary nearly fourfold in their ability to 

 synthesize thiamine. WTien a haplont of low synthetic ability was 

 crossed with one of high synthetic ability, no definite evidence of domi- 

 nance was observed. By making other types of crosses it was found that, 

 in general, the synthetic ability of the Fi haplonts was similar to that of 

 the "parent" haplonts. Yet, when the "parent" haplonts differed 

 widely in synthetic ability, the Fi haplonts did not segregate into the 

 1 to 1 ratio, as would be the case if inheritance were due to a single gene. 

 Single-spore cultures from haploid fruit bodies produced by certain 

 haplonts were more uniform in their ability to synthesize thiamine than 

 were single-spore cultures from diploid fruit bodies of known origin. It 

 was concluded that the ability to synthesize thiamine by L. trahea is 

 genetically controlled, and that the mode of inheritance is complex and 

 not due to a single gene. 



The smuts have received much attention in genetic studies by Stakman, 

 Christensen, and their associates at the University of Minnesota. Such 

 characters as sex, pigmentation, pathogenicity, and morphological fea- 

 tures of the mycelium and spores have been included in the study. Little 

 is known regarding the factors governing the more strictly physiological 

 or nutritional processes. An excellent review of the genetics of the smuts 

 is given by Christensen and Rodenhiser (1940). These authors discuss 

 the work of Goldschmidt, who found that the diploid mycelium derived 

 from two haplonts of different races of Ustilago violaceae was able to 

 attack the hosts which were susceptible to each parent race. This 

 indicates that the diplont contained the combined pathogenic characters 

 of the two haplonts. Hanna (1932) made an interspecific cross between 

 Tilletia levis, with smooth spores and an odor of trimethylamine, and T. 

 tritici, which had rough spores and no odor of trimethylamine. The 

 Fi "chlamydospores" had smooth walls and emitted an odor of tri- 

 methylamine, showing that both characters were dominant. 



