RESPIRATION EXPERIMENTS WITH SWEET POTATOES 
By Heinrich HassEebring and Ton A. Hawkins, 
Plant Physiologists , Drug-Plant, Poisonous-Plant, Physiological, and Fermentation 
Investigations, Bureau of Plant Industry 
INTRODUCTION 
In 1882 Muller (7) / in the course of his classical researches on the accu¬ 
mulation of sugar in plant organs at low temperatures, observed that 
potatoes (Solanum tuberosum) which had been kept for a time at o° C., 
and whose sugar content had in consequence been greatly increased, 
respired much more energetically than potatoes of lower sugar content. 
Even before the experiments of Muller, a number of analogous facts 
were known, all indicating that the respiratory energy of plants is a 
function of their carbohydrate content. Thus, isolated rootlets and 
seedlings deprived of their cotyledons show a rapid decrease in their 
respiration on account of the lack of plastic material normally furnished 
by the cotyledons (12). In etiolated seedlings the respiration curve 
rises at first as the food substances in the cotyledons or endosperm 
become available, and after passing a maximum falls gradually with the 
exhaustion of the food reserve (6, 11). The respiration of isolated leafy 
shoots kept in,the dark sinks rapidly also, but if such shoots are exposed 
for a time to sunlight their respiration is considerably increased (1, 2). 
So also, if the carbohydrate content of etiolated leaves, shoots, or seed¬ 
lings is increased by an immersion of the parts in sugar solutions, respira¬ 
tion is greatly stimulated, although Palladine attributes the increased 
respiration partly to the formation of active proteins produced under 
conditions of favorable carbohydrate nutrition (5, 8, 9). 
Since the sugar content of sweet potatoes (Ipomoea batatas) changes 
greatly in storage, it appeared not unlikely in view of the foregoing facts 
that their respiratory activity would show corresponding changes at 
different seasons. The experiments described in the following pages 
were performed in order to ascertain whether any such correlation exists 
between the seasonal changes in the sugar content of sweet potatoes 
and their respiratory activity, and incidentally to determine if possible 
whether the monosaccharids or the disaccharids of the sweet potato 
furnish the chief material for respiration. The roots were taken from 
the lots stored for experimental purposes under the conditions described 
by the writers in a former paper (4). The details are given in connection 
with the descriptions of the individual experiments. The respiration 
1 Reference is made by number to “Literature cited,” p. 517. 
Journal of Agricultural Research, 
Dept, of Agriculture, Washington. D. C. 
bk 
Vol. V, No. 12 
Dec. 20, 1915 
G—68 
(509) 
