114 Butter: SUGAR IN TUBERS OF SOLANUM TUBEROSUM 
potatoes stored at 0° C., then at 10° C., then at 20° C., and again 
at 10° C., is compared. It will be seen at once that when potatoes 
were placed at 10° C. respiration immediately increased, then 
fell gradually until the potatoes were placed at 20° C., when it 
rose again to the same maximum as before but decreased more 
rapidly and, after being placed at 10° C. again for a short while, 
became almost equal to what it had been when the potatoes were 
stored at 0° C. It should be noted that the experiments just 
recorded were begun after the potatoes had been kept for 28 
days at 0° C., i. e., the potatoes used were rich in sugar. 
Miiller-Thurgau believed that when potatoes containing sugar 
were placed at 20° C. the sugar that disappeared was partly 
used up in respiration, and partly reconverted to starch, as 
the disappearance of the sugar could not be all accounted for 
by the amount of carbon dioxide exhaled. In performing his 
experiments Miiller-Thurgau sliced his potatoes longitudinally, 
using one half for immediate analysis and the other for analysis 
at the end of the experiments. Under these conditions, even 
when the proper corrections for loss of weight due to evaporation 
are made, some of the sugar will undoubtedly go to the formation 
of the suber produced along the cut surface, and not unlikely, the 
increase in the percentage of starch obtained was due to the 
hydration of the cellulose that had been recently or was being 
laid down. The question, however, is deserving of further study. 
OXYGEN 
We have seen that during the rest period sugar may be made 
to accumulate in potatoes by storing the tubers at temperatures 
varying between 0° C. and 6° C., but that at 8°-10° C. the amount 
of sugar (when any was present) remained stationary. The 
relation of the oxygen supply to the accumulation of sugar in 
potatoes therefore may be studied conveniently at 8°-10° C. In 
the experiment which I have performed on this subject I used the 
Sir Walter Raleigh variety of potato and the tubers were placed 
in tubulated bell jars of the usual pattern: 
Bell jar no. 1 contained 1,934 grams of potatoes, and the 
tubules were stopped with cotton, thus allowing a free diffusion 
of air. 
