Dec. 27. 1915 Carbohydrate Transformations in Sweet Potatoes 545 



to compare the changes in the roots during the period immediately after 

 they were dug with those during a subsequent period of the same length. 



The second series of experiments was in all respects like the first except 

 that the potatoes were dug on October 16 and placed in the experimental 

 chambers on October 17 and 18. The length of time of storage was 12 

 days. 



It was the object of the third series of experiments to determine the 

 effect of removal of the vines on the initial carbohydrate changes in the 

 sweet potato. The potatoes used in this series were, therefore, not dug 

 until some time after the vines had been killed. The first frost, which 

 killed the leaves but not the vines, occurred on October 22; a few days 

 later, October 27, the vines were cut off close to the ground, so that from 

 this time there would be no further transfer of materials from the vines to 

 the roots. The potatoes were dug on November 6 and were thereafter 

 treated as described for the other experiments, with the exception that 

 the storage period was 10 days. 



METHODS OF ANALYSIS 



The methods of analysis were essentially the same as formerly de- 

 scribed.* Only a few exceptions need be noted. The samples for moisture 

 determinations v/ere covered with 95 per cent alcohol as before, but the 

 alcohol was evaporated in a drying oven at 50° C. Thereupon the samples 

 were dried to their lowest weight in a vacuum oven in a slow current of air. 

 This procedure gav^e clean, nearly white samples. For the starch deter- 

 minations 10 gm. were weighed out and the whole sample, instead of 

 an aliquot, was extracted, ground, and used for hydrolysis. The sugar 

 samples were put into flasks, which were then nearly filled with 70 per 

 cent alcohol, with the addition of a little calcium carbonate, and boiled 

 for a minute or two. The starch samples were stored, without boiling, 

 in 95 per cent alcohol. 



GENERAL OBSERVATIONS ON THE EXPERIMENTS 



In the experiments described halves of the same sweet potato were 

 compared with each other, the one being analyzed immediately and the 

 other at the end of a 10 to 12 day period of storage. Two questions 

 immediately arise regarding this procedure, which was adopted because 

 different sweet potatoes of the same variety differ much in composition: 

 First, are the halves of the same potato ahke in composition; and, second, 

 do the cut potatoes behave in the same manner as whole potatoes in 

 storage ? 



Miiller-Thurgau ^ in his work on the common Irish potato found that 

 there were only slight differences in the sugar content of the two halves 



1 Hasselbring, Heinrich, and Hawkins, L. A. Physiological changes in sweet potatoes during storage. 

 In Jour. Agr. Research, v. 3, no. 4. P- 331-342. i9is- Literature cited, p. 341-342- 



^Mijller, Hermann, Thurgau. Ueber Zuckeranhiiufung in Pflanzentheilcn in Folge niederer Tempera- 

 tur. Ein Beitrag zur Kenntniss des Stoffwechsels der Pflanzen. In Landw. Jahrb., Bd. ii, p. 751-828^ 



pi. 26. 1882. 



