THE TEMPERATURE OF LEAVES OF PINUS IN WINTER 4I 
for the maintenance of the tree, but there is actually an increase in the 
reserve material during the ''rest period" so called. Mer (17) thirty 
years earlier working with the leaves of Hedera came to a similar 
conclusion. The experiments of both of these investigators were 
made with material growing in the open — Mer at Paris, Sablon at 
Toulouse. Unfortunately neither gives any data as to temperatures. 
How far their results may be applied in a given locality depends upon 
the factors governing photosynthesis in that locality. That they 
hold for the greater part of Japan has been shown conclusively by 
Miyake (18) in the investigations cited above. 
III. Methods 
A. Preliminary Work in igi2-ij 
1. Material and Location. — Since the purpose of this investiagtion 
was to find the internal temperature of pine leaves in winter under as 
nearly natural conditions as possible, cut branches were avoided and 
leaves in situ used. As best suited for the purpose, the species Pinus 
laricio austriaca Endl. was selected. The leaves of this species are, in 
cross section, the largest of the conifer leaves available in this locality. 
The tree used during the preliminary work is about 2.5 meters 
high and is located in the university arboretum about a mile from the 
university campus. A small shed was built near the tree to house the 
apparatus. 
2. Method. — The character of the leaves and the conditions under 
which the work was to be carried out made a thermo-electric method 
the only method possible. In the preliminary work an attempt was 
made to interpret directly into temperature differences, by means of 
a d'Arsonval galvanometer, telescope, and scale, the electromotive 
force produced by the difference in temperature of two thermo- 
junctions, one embedded in the leaf tissue, the other in a thermos- 
bottle kept at a known temperature — usually at 0° C. This method 
was, however, found unsatisfactory. The changes in the resistance 
of the lead wires and the wires connecting the leads with the galvan- 
ometer in the shed, as well as the changes in resistance in the galvan- 
ometer itself, due to changes in atmospheric conditions, made new 
calibrations necessary not only each day, but sometimes several times 
a day. After a thorough test this method was abandoned. 
