1913] BRANNON—OSMOTIC PRESSURE 435 
made. Subsequently it appeared that it was largely due to the 
fact that small specimens were taken from the ice box on that date. 
The size of the potato is of such consequence that the potatoes 
should be selected for uniformity at the beginning of the experiment. 
What the causal agent is has not been determined, but it uniformly 
appeared in the various tests made with the different varieties used 
in these osmotic studies. 
Graph 2 (fig. 2) contains a summary of the readings made in a 
set of experiments extending from January 22, 1912, to July 17, 
1912. A pronounced lift in osmotic pressure in the sap taken from 

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Fic. 2 
the ice box potatoes is well illustrated, and the depression in the 
osmotic pressure in the sap taken from the room potatoes is also 
clearly shown. In the progress of this work there are certain inter- 
esting variations which seem to be related to the question of fil- 
tration of sap and also intimately associated with the size of the 
potatoes from which the sap was secured. As already noted, the 
curve for the unfiltered potato sap ran considerably higher on the 
average than that of the filtered. It was more pronounced in the 
case of the ice box potatoes than in those kept at room temperature. 
The filtered and unfiltered sap from ice box Burbank potatoes 
