OSMOTIC PRESSURES IN THE POTATO PLANT 
TABLE 2. 
Percentage of Water Soluble Salts in Juices. 
Sept. g, igi8. Old plants. 
P2O5 
CI 
SO3 
CaO 
MgO 
Na.O 
K2O 
Total 
Leaves 
.496 
.180 
.128 
.353 
2.260 
•133 
.120 
3.671 
Stalks 
.558 
.192 
.139 
.378 
1.487 
.035 
.359 
3.148 
Tubers 
.821 
.046 
.241 
.394 
I. Ill 
.096 
.071 
2.761 
Sept. Q, igi8. 
Young plants. 
Leaves 
472 
.061 
•235 
.186 
.871 
.044 
.065 
1-935 
Stalks 
.205 
•053 
.040 
.256 
I.OI3 
•073 
•075 
1-715 
The foliage on many, of the old plants was largely dead by September 
18, but the stalks, together with small tufts of leaves, were still green. 
Other plants had lost their foliage entirely and their stalks were of a yellow- 
green hue. The diminution in the osmotic pressure of the sap from these 
stalks that were still green is marked, but it is even more so in the yellow- 
green ones. The sugars were entirely absent. Analyses of the ash of the 
saps appear in table 3. 
TABLE 3. 
Percentage of Salts in Juice of Stalks 
Sept. 18, 1918. 
Old stalks 
Green Stalks 
CaO = .949% 
2.212% 
SO3 = .029% 
-207% 
MgO = 1.364% 
1-815% 
CI .076% 
.142% 
P2O5 = .552% 
.603% 
NazO = .089% 
.142% 
K2O = .088% 
.130% 
3.141% ash. 
5.251% ash. 
It will be seen that as the foliage and stalks die and the tubers mature, 
the latter withdraw from the aerial portions a considerable portion of the 
soluble materials. These results on the ash of the soluble salts in the sap 
agree with those secured by Kellerman (12), noted before. 
The McCormick plants used on September 19 still showed a slightly 
higher osmotic pressure in the stalk sap than in the leaf sap, the sap in the 
upper part of the stalk did not differ materially from that in the lower part, 
the roots exhibited a remarkably low pressure, while the fruit and tubers 
occupied in this respect an intermediate position between the leaves and 
roots. Two of the plants were allowed to transpire in a current of air for 
five hours, and the freezing points of the juice from the leaves and the upper 
part of the stalk were again determined. The incipient wilting had raised 
the osmotic pressure of the leaf sap 3 atmospheres or 39 percent, while in 
