SAP DENSITY AND FREEZING POINTS OF LEAVES. 123 
of the illustration of the instrument used, are a convenient 
means of conducting the sap from the jaws of the vise to 
the test tubes. The saps were placed in test tubes, stop- 
pered with cotton, numbered, and then stored in an ice 
box for approximately twenty-four hours, after which they 
were frozen in exactly the same order in which they were 
collected. Since, according to Dixon and Atkins, the saps 
stored for a period of twenty-four hours have the same 
freezing points as when freshly extracted, it is assumed 
that this represents their normal freezing point. But even 
if this were not so, and the writer has not tried to verify 
their conclusion, then the results will all be in error in 
the same direction, and hence are, for our purpose, quite 
accurate enough. The saps were collected for a period of 
about a week, fortunately accompanied by rather uniform 
weather, mostly clear, although cloudy at times, and not 
accompanied by rains at any time during the experiments. 
However, the weather was exceedingly dry, and it was at 
times difficult to obtain perfectly turgid leaves. All of 
the leaves from which sap was taken, were gathered in 
full sunlight, and, since they were mostly taken between 
2:00 and 4:00 p. M., were from the southwest to the west 
side of the trees and shrubs. Except for some of the 
lower growing shrubs, the leaves were gathered at a point 
from four to five feet from the ground. The variation 
in color observed by Dixon and Atkins was also clearly 
shown by the saps after they had been allowed to settle 
for some time. The color of the sap when first pressed 
out and that observed after settling, 7. e., after the clear 
liquid had separated out from the chlorophyll and sedi- 
ment, was quite variable, but since it had, as far as 
could be determined, exerted no influence on the freezing 
point lowering or had any relation to the results obtained, 
the tabulation of these colors has not been observed in 
this paper. 
The times of collection, together with the dates of 
freezing, are as follows :— 
