SPORULATION 



331 



duction of mature ascospores is greater than the amount required for 

 the formation of perithecia. 



.4 B 



Fig. 68. The effect of biotin starvation on the formation of ascospores by Sordaria 

 fimicola. A, asci from a perithecium developed in a suboptimum concentration of 

 biotin. Note the few mature ascospores and the majority of asci in which no spores, 

 or only aborted ascospores, have formed. B, normal asci with mature ascospores 

 developed on medium with optimum biotin concentration. 



Since the vitamins are not considered as specific reproductive sub- 

 stances, it may be expected that an adequate vitamin supply may be 

 necessary for the formation of asexual spores as well as the sexual fruiting 

 structures. However, it should be kept in mind that asexual reproduc- 

 tion is more nearly like vegetative growth in its requirements than is 

 sexual reproduction. A reduction in the supply of a necessary vitamin 

 to the point where asexual reproduction is inhibited may also allow but 

 little vegetative growth. Piricularia orijzae is deficient for both thiamine 

 and biotin (Leaver et al., 1947). Conidia did not form unless both 

 vitamins were present in the medium. The concentration of biotin 

 could be reduced to such a level that conidial production was inhibited 

 but some mycelial growth was still allowed. In an adequate supply of 

 biotin, growth and sporulation were apparently parallel. It is also 



Table 58. The Effects of Concentration of Glucose and Thiamine upon the 



Number of Conidial Heads Formed by Choanephora cucurbitarum 



(Barnett and Lilly, Phytopathology 40, 1950.) 



Glucose, 

 g. per liter 



25 



25 



25 



2 



Thiamine, 

 Mg per liter 



Conidial heads 

 per plate 



8 



210 



450 



2,000 



