VITAMINS AND UNIDENTIFIED FACTORS 371 



with a major element like potassium (209) or magnesium (230), that 

 sporulation is prevented by deficiencies which do not completely in- 

 hibit growth. That is, sporulation requires more of a mineral than 

 the minimum necessary for measurable growth. 



Much has been made of the repressive effect of added zinc on sporu- 

 lation (38, 113, 152, 165, 246). Toxicity, of course, is possible, but 

 it seems more likely that in the concentrated media used, provision of 

 zinc simply postpones sporulation by allowing more luxuriant vege- 

 tative growth. 



The response of Chaetomium globosum to calcium (21, 22) is an 

 apparent contradiction to the principle that sporulation and growth 

 have qualitatively the same mineral requirements: calcium does not 

 affect dry weight but does increase perithecium formation. The fact 

 that many fungi, including other Chaetomium spp., do respond in 

 growth to calcium and the possibility that calcium is an antagonist 

 rather than a nutrient (Chapter 9) are arguments against immediate 

 revision of the principle. It may be noted that sporulation in Asper- 

 gillus niger is inhibited by high levels of NaCl without any apparent 

 effect on growth (201). 



One rather serious reservation attaches to most of the results men- 

 tioned in this section — sporulation is estimated visually rather than 

 measured quantitatively. A second limitation is that most of the work 

 has been with Aspergillus niger; study of other organisms might cause 

 us to modify some of the conclusions now accepted. 



9. VITAMINS AND UNIDENTIFIED FACTORS 



Under this head, we consider only substances which exert a non- 

 specific effect; hormones and hormone-like substances are taken up in 

 the next section. 



The data available show that most fungi which require biotin or 

 thiamine need more of the vitamin for adequate sporulation than they 

 do for measurable vegetative growth (17, 134). Thus, Sordaria fimi- 

 cola in a medium without biotin makes about one-third maximal 

 growth but does not form perithecia unless the vitamin is supplied; 

 in this species biotin deficiency results in abortion or failure to mature 

 of ascospores (16). 



However, one cannot specify an "optimum" level of a vitamin with- 

 out reference to other constituents of the medium. Ceratostomella 

 fimbriata, for example, requires thiamine in proportion to the total 

 concentration of the medium (17). Conversely, it is well established, 

 for numerous fungi, that provision of thiamine raises the level of 



