OSMOTIC PRESSURE IN POTATOES 
CONTRIBUTIONS FROM THE HULL BOTANICAL LABORATORY 177 
M. A. BRANNON 
(WITH FOUR FIGURES) 
During recent years the problems of periodicity, dormancy, and 
after-ripening have been investigated by numerous plant physi- 
ologists. Among the numerous questions involved, that of osmotic 
pressure has a prominent place. Naturally, the study of osmotic 
pressure in living cells affords a difficult and intricate field of 
research provided the direct method of measurement is employed. 
If an indirect method, such as the cryoscopic, be used, the principal 
difficulty is to secure sufficient sap, in the event that the freezing 
temperature is determined by the Beckmann apparatus. The 
potato tuber satisfies this requirement in an excellent way. This 
paper is intended to present some of the results obtained in the 
study of the osmotic pressure of the sap taken from potato tubers 
kept at room temperature and in ice boxes. In this brief paper, 
there is no intention of giving a review of literature pertaining to 
the subject of osmotic pressure in its relation to after-ripening. 
The literature on after-ripening has been completely presented by 
Miss ECKERSON in a recent paper.” 
Methods 
In studying osmotic pressure in potatoes, an effort was made 
to reduce the experimental work to a single factor and that the 
limiting factor, heat. Various kinds of potatoes were used, such 
as the Burbank, Russet Burbank, Triumph, Snowflake, and 
Dakota Red. The potatoes were gotten in the autumn, wrapped 
in paraffine paper, and placed in two collections. One was buried 
in dry sand or gravel and kept at room temperature of 22-25" C. 
* ECKERSON, SopHIA, A physiological and chemical study of after-ripening. 
13; 
Bot. Gaz. 55:286-299. 19 
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