358 



[Vol. 10 



ANNALS OF THE MISSOURI BOTANICAL GARDEN 



10 days of incubation, yet the NH a .N content of the culture fluid 

 was only 0.14 mgm. per 50 ml. 



To recapitulate, it is seen that the data throw some light on 

 the forms of N which are directly utilizable and most serviceable 

 for the fungi. Judging by the maximum dry weight attained, 

 and disregarding the effects of acidity and other factors on metab- 

 olism, peptone in the presence of dextrose was the superior N 

 source for all 3 fungi, whereas peptone in the absence of suga 



Z Z + S 6 T 6 9 n? 



Fig. 18. Total N in 50 ml. media. Sphacropsis malar um. 



was distinctly inferior. This supports the 



brought out 



on pp. 350-351 that amino acids and even "peptid" units may 

 be directly assimilable if they are actually found as such in the 

 proteins of the fungi. To this must be added that an available 

 carbon source must be present 

 necessary for the cementing of these build 



to supply readily the energy 



ng stones. It is 

 evidently difficult to obtain this energy by deamidization of the 



peptone com 

 complex. Fo 



ments and utilization of the non-nitrogenous 

 the same reason amino acids serve but noorlv as 



sources of both C and N, as has been shown by several investi- 

 gators. However, it is probable that the NH ■ group of the amino 

 acids is a very readily available form for those organisms that 

 possess deamidizing enzymes sufficiently strong to split off this 



readily. Waksman ('18) found indicat 



such 





