406 
Lewis and Tuttle . — Osmotic Properties of some 
The ecological side of the problem has been attacked by Harris and 
Lawrence ( 1 ), working on the osmotic pressures of Jamaican rain-forest 
vegetation. These authors found that vegetation of different ecological 
habitats possessed different osmotic pressures, but no information is given 
in their work as to the relative proportion of electrolytes and non-electro- 
lytes in the several types they investigated. 
It seems probable that ability to withstand low temperatures depends 
entirely upon the organization and biochemical characters of the cells. 
Although attempts have been made to recognize modifications of structure 
which would enable aerial or subaerial organs to withstand low temperature, 
none have been found whose presence would render the plant resistant. 
An increase in the concentration of the cell sap will lower the freezing- 
point, but this seldom amounts to more than T C. Muller ( 2 ) has shown 
that living plants usually have a lower freezing-point than the expressed 
sap. The fact that the actual freezing-point of the cell is lower is due to 
surface tension forces, such as capillarity and imbibition. Mousson ( 3 ) 
found that in a capillary tube of not mot^ than 0*4 mm. diameter the 
freezing-point of water was lowered o*i° to 0-3° C. In order that sub- 
cooling may take place a localized formation of ice must be avoided. 
When contact with ice is avoided sub-cooling is observed in water. Thus 
Dufour ( 4 ) obtained the sub-cooling of — I2°C. in small drops of water 
floating in a mixture of almond oil and chloroform. 
In the experiments carried out by Miiller-Thurgau, leaves were wrapped 
round the bulb of a sensitive thermometer and inserted in a freezing 
mixture with the thermometer scale projecting outside. With this method 
the temperature sinks until the maximum degree of sub-cooling is reached, 
and then rises to the true freezing-point, when ice formation takes place, 
after which it falls gradually. According to Pfeffer the sub-cooling in most 
plants is not more than — 3 0 to — 4 0 C. It is important to remember that 
most previous experiments have been performed with plants living in com- 
paratively temperate climates, and results obtained in this investigation (in 
Western Canada) with plants subjected to long periods of — 40° to — 50° F. 
have some bearing on the question. 
Scope of Work. 
The scope of the present investigation may be indicated as follows : 
1. To determine the osmotic pressure, relative amount of electrolytes 
and non-electrolytes, and sugars in a few typical plants living at low 
temperatures from the autumn throughout the winter. 
2. To determine the temperature at which ice formation actually takes 
place in the living cells of the tissues. 
3. To observe the condition of the cell contents at low temperature. 
The materials chosen for investigation were Pice a canadensis (Miller) 
