A note on the significance of sugar in the tubers of 
Solanum tuberosum 
O. BUTLER 
(WITH PLATE 2) 
Sugar accumulates in the tubers of the potato during the rest 
period when they are subjected to low temperatures, and, at least 
this is the general opinion, at the time of germination. In other 
words sugar develops at a time when the various vitalistic phe- 
nomena are inactive and again when the life processes are pro- 
ceeding actively. 
I 
During the rest period two factors influence the accumulation 
of sugar in the tubers of the potato: temperature and oxygen 
supply. Both these factors may act independently of one another 
or additively. I shall, however, for convenience, consider them 
separately. 
TEMPERATURE 
The effect of temperature on the accumulation of sugar in 
potato tubers was studied years ago by Miiller-Thurgau* and, 
as the results he obtained have not been disproved, I will simply 
briefly review them, adding some data of my own in confirmation. 
The belief is very tenaciously rooted in the popular mind that 
a potato becomes sweet only when it is frozen. A frozen potato 
never becomes sweet, moreover a potato does not freeze at 0° C., 
whence probably the origin of this notion. Potatoes, in fact, 
may be stored at 0° C. for a period of time without being injured, 
Miiller-Thurgau having kept them at this temperature in some 
of his experiments for as long as one hundred days.. 
Taking 0° C., then, as the lowest temperature at which potatoes 
may be safely stored, Miiller-Thurgau found that when the rates 
of sugar accumulation at 0° C., 3° C., and 6° C. were compared 
* Miiller-Thurgau, H. Ueber Zuckeranhdufung in Pflanzentheilen in Folge 
niederer Temperatur. Landw. Jahrb. 11: 757-828. Vie, 
110 
