408 Lewis and Tuttle. — Osmotic Properties of some 
To minimize any marked variation of the sugar content due to variation 
in photosynthesis at different times of the day, all material was collected 
at % p.m. 
Meteorological Conditions. 
Records of the temperature were kept from January onwards by means 
of a Casella Recording Thermograph. The instrument was fixed on a wall 
facing north, about sixty feet above the ground. The temperatures 
recorded were probably slightly above those obtaining at the level of the 
ground. A reduced record of the maximum and minimum temperature 
curve is given in Graph I. As the instrument only recorded down to 
+ io°F. the breaks in the diagram indicate periods below this temperature. 
The minima are recorded in figures in these blanks. 
The first part of the winter was unusually free from low temperatures, 
the lowest temperatures coming in February and March. 
Records of Osmotic Pressures, &c. 
All the material was obtained from the same habitat — a slope facing 
north. Trees of Picea of approximately the same age were used through- 
out — about fifteen years. To obviate any discrepancy due to individual 
differences of pressure in the trees, branches were cut from several trees, 
brought into the laboratory, and the leaves cut off. To eliminate any error 
due to differences in osmotic pressure of leaves of 'different ages only those 
from the previous year’s shoot were taken. The leaves were then frozen 
and thawed in the manner already described and the cell sap expressed. 
The osmotic pressure was determined immediately, and then the conduc- 
tivity, the whole process for one observation taking about three hours. The 
sugar estimation in some cases was made the following day, and in that case 
the sap remained frozen during the interval. 
The depression of the freezing-point and the corresponding pressures 
in atmospheres are recorded in the tables and in the ordinates of the graphs. 
The figures in column C give the conductivity of the sap at 37 0 C. The 
figures under A e are calculated f rom those under A and C, and represent 
the depression in freezing-point of solutions of potassium chloride having 
the same conductivity as those observed for the sap. They represent the 
total A due to electrolytes. The cokimn A — A e represents the total A 
due to the presence of non-electrolytes in the sap. This method was used 
by Dixon and Atkins (8), and gives clear indication of the main changes 
going on in the cell. 
The material for the observations on Populus , Linnaea , and Pyrola 
was obtained from the same habitat as Picea. The respective readings are 
given in Tables I to IV and recorded in Graphs II to V. The atmospheric 
