JOURNAL OF AM MAL RESEARCH 
Vol. XXI Washington, D. C., May 16, 1921 No. 4 
GLUCOSE AS A SOURCE OF CARBON FOR CERTAIN 
SWEET POTATO STORAGE-ROT FUNGI 
By J. L. WkimF.r, Assistant Pathologist, and ,L. L. Harter, Pathologist, Cotton, 
Truck, and Forage Crop Disease Investigations, Bureau of Plant Industry, United 
States Department of Agriculture 
INTRODUCTION 
The fact that fungi do not have the power to manufacture their own 
carbohydrates has long been known, and it has been demonstrated 
many times that carbon in certain chemical combinations is more avail¬ 
able than in others. Some microorganisms can utilize cane sugar, 
while others can use only the invert sugars, and still others thrive upon 
organic acids, weak alcohols, and other organic compounds. Both cane 
sugar and invert sugars are commonly present in the sweet potato, and 
hence it is these two forms of carbon which should receive attention in 
the study of this phase of this problem. 
Butkewitsch (j) 1 showed that Rhizopus nigricans Ehrb. could not 
utilize cane sugar as such, and, further, that this organism produced no 
invertase. On the contrary, Pringsheim and Zemplen (26) found that 
although R. tonkinensis Vuill., Mucor javanicus Wehm., Penicillium 
purpurogenum Fleroff., P. africanum Doeb., and P. brevicaule Sacc., 
could not use cane sugar directly, they did possess the power to invert 
it. Ritter ( 28) worked with several of the same forms and demon¬ 
strated that some of the organisms were able to invert cane sugar while 
others were not. He showed further that when ammonium nitrate or 
ammonium sulphate were employed as a source of nitrogen, nitric acid 
or sulphuric acid was formed, which probably inverted some of the cane 
sugar, thus making it available as a source of carbon for the fungi. 
The investigations of Hasselbring and Hawkins (75) showed that the 
cane sugar, and to some extent the glucose content of the sweet potato 
in storage, increased with a decrease in starch from the time of digging 
in October until March or April, when there was a reverse of the process. 
They pointed out, also, that the amount of glucose in the sweet potato 
is always small as compared with that of the cane sugar. It is believed 
by many that the susceptibility of the sweet potato to decay likewise 
increases as the season progresses. This might seem to imply that 
there is some correlation between the sugar content of the potato and 
1 Reference is made by number (italic) to “Literature cited,” p. 208-210. 
Journal of Agricultural Research, 
Washington, D. C. 
xt 
• (189) 
Vol. XXI, No. 4 
May 16, 1921 
Key No. G-229 
