780 



Journal of Agricultural Research 



Vol. XX, No. 10 



Experiment 2. — In this set of experiments sweet potato bouillon 

 was compared with Czapek's modified nutrient solution, the latter con- 

 taining different amounts of starch and glucose as a source of carbon. 

 The reducing sugars were determined in each series before inoculation 

 and after the fungous growth had been removed, the enzyms in the solu- 

 tions being inactivated at the end of the growth period by autoclaving 

 the solutions. The cultures were incubated for 10 days at 35 ° C. The 

 hydrolytic power of the enzym was determined by the use of 0.25 gm. 

 of powder in 100 cc. of a 0.5 per cent starch paste solution. The time 

 of hydrolysis was 1 8 hours at 40 C. (Table XIV.) 



Table XIV. — Source of carbon in Czapek's modified nutrient solution, amount 0/ 

 reducing sugars before and after the growth of the fungus, and the hydrolysis by the 



enzym powder 



[Expressed in milligrams per 10 cc. of the substrate] 



» Solutions a, b, and c were Czapek's nutrient solution; d was sweet potato bouillon. The reducing sugar 

 in b and c before inoculation was glucose. 



The starch was not determined, but it was shown to be present in series 

 a, c, and d by iodin before the solutions were inoculated. When the 

 fungous growth was removed the starch had all disappeared in series a 



and d. 



From the results it is seen that the largest amount of hydrolysis took 

 place with mycelium grown on sweet potato bouillon (d), where reducing 

 sugars and starch both were originally present. On the other hand there 

 was considerably more hydrolysis with mycelium grown on starch alone 

 as a source of carbon (a) than where glucose was used alone (b) or in 

 combination with starch (c). 



The reducing sugars in series b, c, and d were considerably less at the 

 end of the growth period than at the outset, showing that the fungus 

 made use of reducing sugars or had converted them into other sub- 

 stances.possibly alcohol, acids, etc. No starch remained in the solutions. 

 In series a the starch had entirely disappeared, but a small amount of 

 reducing sugar was present. In this case also the fungus had either used 

 a considerable amount of carbohydrate or had converted it into other 

 compounds. 



The fungus made the best growth in series d, but it was good in all 

 and fruited abundantly in each of the solutions. 



