326 



PHYSIOLOGY OF THE FUNGI 



glucose and potassium nitrate are unfavorable for the production of 

 perithecia by N. crassa. 



Table 56. The Effect of the Carbon-Nitrogen Ratio of the Medium on the 

 Production of Perithecia by Neurospora crassa 

 Production rated on scale of 10. Age, 11 days. (Westergaard and Mitchell, 

 Am. Jour. Botany 34, 1947.) 



Micro essential elements. Steinberg (see references in Chap. 5) found 

 the sporulation of Aspergillus niger to be depressed by the omission of 

 various of the essential elements. Lockwood and Ward (1936) found 

 that Rhizopus oryzae sporulated on the thirteenth day of incubation when 

 zinc was not added to the medium. When zinc was added, sporulation 

 occurred on the third day of incubation. In general, when any essential 

 element is low, sporulation tends to be depressed before growth is 

 inhibited. 



Specific reproductive factors. While many factors may influence 

 reproduction, there is little evidence that the fungi need specific chemical 

 substances to induce reproduction. Such factors, however, do exist 

 among certain of the Phycomycetes. 



Four specific regulatory substances, called hormones (Raper, 1942, and 

 Raper and Haagen-Smit, 1942), were shown to initiate and control sexual 

 reproduction of Achlya hisexualis. A specific substratum is required for 

 the production of hormone A in large quantities. Hempseed allows a 

 2- to 10-fold production of hormone A over that produced by similar cul- 

 tures grown upon corn, rice, lentils, or other substances. Hormone A 

 has been concentrated 70,000-fold but has not yet been obtained in pure 

 form. This concentrate of hormone A is active in dilutions of 1 X 10^^^. 



Sexual reproduction in Phytophthora cactorum was greatly stimulated by 

 an extract of garden peas (Leonian, 1936). This substance had no 

 growth-promoting properties. It was concluded (Leonian and Lilly, 

 1937) that the sexuality factor was none of the known vitamins, and that 

 it probably was not carotene or xanthophyll, although it was concentrated 

 by methods which would concentrate these substances. When vigorous 



