632 
Journal of Agricultural Research 
Vol. XXI, No. 9 
growth of this fungus in nutrient solutions with cane sugar as the only 
source of carbon have shown that this substance is used only sparingly. 
This fact, together with the evidence contained in the data already 
submitted, indicates three possibilities: First, that the fungus can utilize 
to a better advantage cane sugar when other carbohydrates are present; 
second, that in the living potato the host under the stimulation of the 
fungus inverts the cane sugar; and third, that the acids produced by 
the fungus invert the cane sugar. The following experiments were 
designed to throw some light on this phase of the subject. 
In cooked potatoes. —Large sweet potatoes were cut longitudinally 
into two parts and pared to equal weight. The two halves were cut in 
small blocks into separate flasks and sterilized by steaming on three 
consecutive days. One flask was inoculated with Rhizopus iritici and 
the other one held as a control. They were both kept in an incubator 
held at a constant temperature of 30° C. After 15 days the starch, cane 
sugar, and reducing sugar of the control and inoculated flasks were 
determined according to the'method already described. The results of 
these analyses are shown in Table III. 
Table III .—Carbohydrate content of inoculated and uninoculated cooked sweet potatoes a 
Experi¬ 
ment No. 
Sample. 
Reducing 
sugars as 
glucose. 
Total 
sugars as 
glucose. 
Cane sugar. 
Starch. 
670 
/Control. 
45 - 5 6 
O 
122. 77 
n 00 
73-36 
8. 569 
62. 9O 
99 - 565 
\ Inoculated. 
740 
f Control.. 
AA 2 T 
y* & 
T TO A 9 
* 5 - 5 2 5 
97-477 
14. 424 
\ Inoculated.. 
7 A 02 C 
J. IV. 
73- 685 
O 
° Calculated to milligrams per gram of original wet weight. 
An inspection of Table III shows that the starch, cane sugar, and 
total sugar content of the inoculated material was greatly reduced, 
the cane sugar having disappeared entirely in experiment 740. It 
seems from these results that the fungus can either use cane sugar 
directly or convert it into some other substance before using. With 
respect to the reducing sugars the results of the two experiments do 
not parallel. In experiment 670 no reducing sugar remained in the 
inoculated flask, whereas in experiment 740 there was an actual increase 
over that of the control. This apparent discrepancy may be explained 
at least in part if one takes into consideration the growth of the fungus 
in the two cases. It was previously pointed out that glucose is an 
excellent source of carbon for this fungus, supporting in a nutrient solu¬ 
tion an abundant mycelial growth. The growth of the mycelium in 
the first experiment was very luxuriant, about half filling a 2-liter 
flask, while in the second very little aerial growth took place. In view 
of these facts it is likely that in the former case the reducing sugars 
