RESPIRATION EXPERIMENTS WITH SWEET POTATOES 



By Heinrich HassElbring and LoN 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 0° 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 Miiller, 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 (i, 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 



• Reference is made by number to "Literature cited," p. 517. 



Journal of Agricultural Research. Vol. V, No. 12 



Dept. of Agriculture, Washington. D. C. Dec. 20. 191S 



bk G— 68 



(509) 



