RESPIRATION AND CARBOHYDRATE CHANGES PRO¬ 
DUCED IN SWEET POTATOES BY RHIZOPUS TRITICI 
J. L. WeimEr, Assistant Pathologist, and L. L. Harter, Pathologist, Office of Cotton, 
Truck, and Forage Crop Disease Investigations, Bureau of Plant Industry, United 
States Department of Agriculture 
INTRODUCTION 
These investigations had for their purpose to determine (i) the relative 
rate of respiration, as measured by the carbon dioxid (C 0 2 ) given off by 
the two halves of sweet potatoes, one of which was rotted by Rhizopus 
iritici Saito, and (2) how the starch, cane sugar, and reducing sugar 
content of the two corresponding halves differed at the end of the experi¬ 
ment. It was believed that an insight into the physiological changes of 
the host brought about by the fungus might be obtained by experiments 
in which the carbohydrate content and respiration were determined 
simultaneously. 
METHOD OE EXPERIMENTATION 
RESPIRATION 
The measure of the C 0 2 output was determined from the corresponding 
halves of the same root by four separate experiments. Large, sound 
sweet potatoes were carefully washed, cut in two longitudinally, and 
pared until the two parts had the same weight. A small “well” was 
made in each half by means of a cork borer about 1 cm. in diameter. 
One half was inoculated by pouring a 24-hour growth of the organism in 
sweet-potato decoction (about 2 cc.) into the “well,” and an equal 
volume of sterile water into the “well” of the control half. The two 
halves were then put into separate air-tight desiccators which served as 
respiration chambers through which C0 2 -free air was drawn. The C0 3 
was collected in trap bottles containing barium hydroxid (Ba(OH) 2 ) and 
determined as barium carbonate (BaC0 3 ). The method used for the 
removal of the C0 2 from the air and for its collection and subsequent 
determination is essentially the same as that used by the writers (5) 1 in 
the study of the respiration of fungi in nutrient solutions, to which the 
reader is referred for details. The respiration chambers were kept ill 
an incubator maintained at a constant temperature of 30° C. The C0 2 
given off was determined every 24 hours. By this method decay of the 
inoculated half was evident in 24 to 48 hours and usually complete in 
about 3 days. As soon as decay was complete the two halves were 
removed from the respiration chambers, weighed, and prepared for 
analysis. 
1 Reference is made by number (italic) to “Literature cited,” p. 634-635. 
Journal of Agricultural Research, 
Washington, D. C. 
yt 
(627) 
Vol. XXI, No. 9 
Aug. 1, 1921 
Key No. G-241 
