Plant Cells at Low Temperatures . 
411 
Table IV. Pyrola rotundifolia. 
Date. 
A. 
P. 
A e . 
A — A e . 
C x io 5 . Sucrose %. Maltose / 
Glucose % 
Dec. iq 
2*2 22 
26.69 
— 
— — 
— 
— 
| 29 
I.863 
22.42 
O.223 
1.640 
986 — 
— 
— 
Feb. 8 
I.992 
23.94 
0*276 
1.716 
1186 0.12 
1. 21 
0.00 
April 1 1 
I.43O 
17.20 
0-l8l 
1.249 
780 0.00 
0.11 
o -37 
June 4 
I.O45 
I2.58 
O.239 
0.806 
1028 0.00 
0-00 
0.25 
Total Sugars 
Feb. March April May Jui 
Graph V. Pyrola rotundifona (leaves). 
Amount of Under-cooling and A of Leaves. 
Experiments were made to ascertain the temperature at which ice first 
appears in the leaves of Pice a, Linnaea , and Pyrola. Pice a leaves were 
found unsatisfactory to use for this purpose, as they could not be packed 
tightly round the bulb of the thermometer. Linnaea leaves are too small 
for successful use, and most of the observations were carried out with the 
leaves of Pyrola . 
Experiments have been carried out by Miiller-Thurgau on the freezing- 
point of cell sap in situ by either placing the bulb of the thermometer in 
a succulent tissue such as potato, or wrapping the bulb with the leaves to be 
tested. This method, while not yielding results comparable in accuracy to 
those obtained by placing the Beckman thermometer in a solution, is still of 
considerable value, as it is capable of indicating the amount of under- 
cooling which the minute volume of sap in the cell vacuole is capable of 
undergoing without the formation of ice. That the amount of sub-cooling 
in minute volumes, when contact with ice is prevented, may be much greater 
