SPORULATION 329 



lium next to the Aspergillus colony soon shows stimulated growth, which 

 is followed by the formation of abundant perithecia in this area. Since 

 we know that Sordaria is deficient for biotin and requires an exogenous 

 supply of this vitamin for reproduction, we may assume that the stimulat- 

 ing effect is due to the extra biotin produced by A. rugulosus diffusing into 

 the medium. 



Vitamins. Many fungi cannot synthesize suflricient amounts of certain 

 vitamins and must depend upon an outside source of these vitamins for 

 optimum growth. Since many nutritional factors may influence both 

 growth and reproduction, it would be logical to expect that the vitamin 

 supply would affect the reproduction of vitamin-deficient fungi. Robbins 

 and Ma (1942) ventured the opinion that, although the sex organs of 

 certain deficient fungi were formed only in the presence of the growth 

 factor for which these fungi were deficient, they were doubtful if there 

 was any direct relation between vitamin supply and the formation of 

 sex organs. They regarded the failure of Ceratostomella pluriannulata to 

 produce perithecia in the absence of thiamine to be a disturbance of the 

 physiology of the fungus and ventured the prediction that the formation 

 of sex organs in other deficient fungi would be found associated with the 

 vitamins for which the fungi was deficient. 



Melanospora destruens is able to grow in the presence of biotin as the 

 only growth factor, but it produces perithecia only when thiamine, too, is 

 added to the medium (Hawker, 1939). The relationship between the 

 amount of sugar and the amount of thiamine necessary for maximum 

 fruiting is clearly brought out by the thiamine-deficient fungus, C. 

 fimbriata (Barnett and Lilly, 1947a). Whether perithecia are formed on a 

 given medium is determined by the amount of thiamine relative to the 

 amount of food in the medium (Table 57). In a reduced supply of sugar 

 the concentration of thiamine necessary to induce fruiting is also reduced. 

 The abundance of perithecia is conditioned both by the amount of thia- 

 mine and by the amount of nutrients. Less thiamine is required for 

 vegetative growth than for the production of perithecia. A similar rela- 

 tion between amounts of sugar and biotin and sporulation of Memnoniella 

 echinata was described by Buston and Basu (1948). It should be noted 

 from Table 57 that, in a medium high in sugar but low in thiamine, no 

 perithecia were formed even though as much as 30 mg. of mycelium was 

 present. On the other hand, perithecia were produced on as little as two 

 mg. of mycelium when the medium contained the same amount of thia- 

 mine but was very low in sugar. These results are not in accord with the 

 idea that vigorous or abundant mycelium is essential to the formation of 

 perithecia; they indicate a more direct relation between vitamin supply 

 and sexual reproduction. 



This direct relationship may be further illustrated by a simple experi- 



