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loses water from these parts at such a high rate on hot days that these 
portions are often found to be wilted. 
A large dahlia plant with almost full grown flower buds, used on August 
27, seemed to be at an osmotic equilibrium. 
Fig. 2. Potato leaflet, percentage of water in various portions of the lamina. 
Chicory plants (August 28) showed an osmotic pressure of almost two 
atmospheres more in the leaf than in the root sap, with the stalk sap inter- 
mediate between the two. Chicory behaved in every way as would be 
expected if, as a matter of fact, osmotic pressure is the cause of the upward 
sap flow. 
Heavy rains occurred during early September, cool weather followed, 
and the older potato plants that had not entirely succumbed to tip-burn 
began to resume growth. Cryoscopic readings were taken on September 9 
of the juice from an old plant and from some young plants growing in a 
parallel row since the first week in August. The striking features at this 
time were the relative pressures in the leaves and stalks, the pressure in the 
tubers having remained about constant. The osmotic pressure in the 
leaf sap had greatly increased, so much so, in fact, that it exceeded that of 
the stems by 0.77 atmosphere. The young plants corroborated the readings 
of August 7 and 8, the leaf sap pressure being greater than that of the stalks. 
The increase in pressure in the old plant seems largely due to the inorganic 
salts soluble in the cell sap, since the sugars were conspicuously absent at 
this time. The cooler weather and lack of sunshine were probably respon- 
sible for the latter condition. A complete analysis was made of the ash of 
the sap used in these cryoscopic determinations (table 2). 
