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Walter Stiles 
ovina, and Lythrum virgatum, the osmotic pressure of the cells of the 
root was always higher in the plants of any one species growing in 
a drier soil than in roots of plants of the same species growing in a 
soil of higher water content. Similar relations between the water 
content of the soil and the osmotic pressure of the cells of root and 
shoot of maize have been found by McCool and Miller (1917) by the 
expressed sap method. 
Iljin, Nazarova and Ostrovskaja found that the osmotic pressure 
of the cells of the root is no criterion of the osmotic pressure of the cells 
of the leaves. They come to a conclusion similar to that in regard to the 
influence of the water content of the soil on the osmotic pressure of 
the cells of the root, namely, that the water content of the air sur¬ 
rounding the leaves influences the osmotic pressure of the leaf cells: 
the higher the water content of the air the lower the osmotic pressure 
of the leaf cells. Thus leaves of the same plant, for example, Senecio 
doria, Centaurea scabiosa and Sanguisorba officinalis, had all the same 
osmotic pressure in their cells when growing in the open and therefore 
with all the leaves under the same external conditions as regards 
moisture, but when growing among grass the lower leaves always gave 
lower values of the osmotic pressure than the upper leaves. Drabble 
and Lake (1905,1907) also found by the plasmolytic method higher 
osmotic pressures in the epidermal cells of leaves of those plants 
most subjected to factors tending to loss of water by transpiration. 
Confirmatory evidence of the influence of water content of the 
soil on the osmotic pressure of the plant sap is forthcoming from the 
results of Pringsheim (1906), Meier (1915), Ursprung and Blum 
(1916 c) and Iljin, Nazarova and Ostrovskaja (1916). Plants of a 
number of species were grown by these various investigators under 
different conditions of humidity and the osmotic pressure of the sap 
of the various experimental plants examined. The result is quite 
general that higher water content of the environment corresponds 
with lower osmotic pressure of the cell sap, and vice versa. Even as 
long ago as 1884 de Vries recorded a higher osmotic pressure for 
shoot apices of Helianthus tuberosus after dry weather than after a 
long period of daily watering. 
An increase in the concentration of substances dissolved in an 
aqueous medium is of course equivalent to a decrease in the water 
content. From the observations just recorded it is therefore not sur¬ 
prising to find that plants growing in strong solutions of osmotically 
active substances generally exhibit an increase in the osmotic pres¬ 
sures of their cell sap. Thus Janse (1887 a) showed that the osmotic 
