776 



Journal of Agricultural Research 



Vol. XX, No. jo 



Table XI. — Amount of reducing sugars and starch present in solutions a and b at stated 



intervals of time 



[Expressed in milligrams per 10 ce. of solution] 



Solution a. 



Reducing 

 sugars. 



Starch. 



Solution b. 



Reducing 

 sugars. 



Starch. 



Oct. 27 



2 9 



3i 



Nov. 3 



5 



7 



10 



12 



3 ('controls) 

 12 (controls) 



o 



5-3 

 21. 7 

 46. o 

 61. 4 

 °5-3 

 75- o 

 75-8 

 o 



III. o 



103.0 

 83.0 



59- o 

 41. o 



38.5 



25.2 

 23-4 



5-8 

 34-6 



35- 2 

 21. 6 

 14. o 



7-7 

 6.0 



106. o 

 96. o 

 47.0 



24. o 



25. o 



23.8 



22.8 

 21. 6 



From Table XI it is seen that in two days reducing sugars in excess of 

 those used by the fungus were produced with a decrease in the amount of 

 starch. In the a solution the reducing sugars gradually accumulated to 

 the end of the experiment, while the amount of starch decreased, showing 

 that the fungus did not use a corresponding amount of the reducing sugars 

 formed. On the other hand, in solution b the reducing sugars increased 

 up to November 3 and then decreased to the close of the experiment, 

 while the starch decreased rapidly to November 3 and very little there- 

 after, which suggests that hydrolysis was slowed up as it approached 

 the end point and did not keep pace with the demands of the fungus 

 for reducing sugars. This condition is reflected in the amount of dry 

 matter formed, which is about twenty-four times greater in solution b 

 than in solution a. The amount of starch in the two solutions at the 

 close of the experiment was practically the same. It seems, then, that 

 an extracellular amylase was promptly secreted by the fungus and that 

 it hydrolyzed the starch in excess of the needs of the fungus in one case 

 (a) to the close of the experiment and in the other until November 3, 

 when the reducing sugars consumed exceeded those produced by the 

 hydrolysis of the starch. 



Why the difference in the composition of the two solutions plays such a 

 fundamental role in the growth of the fungus can not be answered. As 

 previously stated, solution a derives its nitrogen from sodium nitrate 

 and solution b from ammonium nitrate. The growth in the latter case 

 was many times greater than in the former. Since solution a was vir- 

 tually Czapek's nutrient solution, it was tried at the outset for other 

 work of a similar nature and was later modified by the substitution of 

 ammonium nitrate for sodium nitrate. The solution so modified gave a 

 luxuriant growth of mycelium. Solution a, however, apparently had 

 no inhibitory action on the amylase, so that hydrolysis of the starch went 

 on unhindered. 



