NITROGEN NUTRITION 



369 



Carbohydrate concentration *- 



Figure 2. The response of growth and fruiting to carbohydrate concentration. 

 Mi and F lt mycelial growth and fruiting, respectively, with a readily available 

 carbohydrate; M z and F 2 , the same with a more slowly available carbohydrate; M 3 

 and F 3 , the same with a very slowly utilizable carbohydrate. From Hawker (140), 

 by permission of the University of London Press, Ltd. 



centration of hexose. This point is shown admirably in Figure 2, 

 from Hawker (140). 



This principle explains many of the effects of particular carbon 

 sources on reproductive activity. Thus, the optimum sucrose concen- 

 tration for fruiting in Melanospora destruens is ten times that in M. 

 zamiae, indicating — and this is borne out by sucrase assays — that the 

 latter species utilizes sucrose much more rapidly than the former (141). 



Hawker (137, 138) has suggested that the favorable effect of sucrose 

 is in part to be attributed to the formation of phosphorylated hexoses 

 from it by the fungus. This, it must be admitted, seems unlikely and 

 is certainly not established by data available at present; phosphory- 

 lated compounds have, however, been tentatively implicated in studies 

 on stimulation by contaminating organisms (p. 372). 



7. NITROGEN NUTRITION 



The concentration of the nitrogen source in the medium is impor- 

 tant for fruiting, i.e., an optimum concentration can be determined 



