THE TEMPERATURE OF LEAVES OF PINUS IN WINTER 65 
with absolute alcohol and ether to remove the fats, and then with a 
solution of chloral-iodine and potassium iodide. During the autumn 
and through December the leaves of Pinus laricio austriaca Endl. only 
were examined. Later other species were added. From five to ten 
leaves were examined in each case. 
In the leaves of Pinus laricio austriaca starch remained abundant 
in mesophyll, endodermis, and transfusion tissue throughout October 
and November. But leaves collected December 2, after a period of 
seven dark, rainy days — maximum temperature for the entire period 
14° C. and the mean 6.7° C. — showed, when examined, no starch in 
the mesophyll and only a small amount in the endodermis. Leaves 
collected from the same branch December 4 — maximum temperature 
11.6° C. and the mean 6.7° C. — showed a small amount of starch in 
the mesophyll, endodermis, and transfusion tissue. On December 11, 
the temperature, in the meantime, having dropped to a minimum 
of — 7° C. and a maximum of 3° C, the starch had entirely disap- 
peared from all the tissues. Starch was again found on December 12 
in the mesophyll, endodermis, and transfusion tissue, and in greater 
abundance on the following day, the temperature having risen to a 
maximum of 12 ° C. 
Since the temperature on December 4 was colder by several degrees 
than that of the preceding days, the reappearance of starch could 
not be due to a regeneration from sugar already present in the leaf, 
but must have been the result of photosynthesis. On December 13, 
however, the maximum temperature had risen 9° C. above that of 
December 11, and the reappearance of starch may have been the 
result, in part at least, of a regeneration of starch from the sugar 
present in the leaf, due to an increase in temperature. 
When next examined, December 20, starch had entirely disappeared 
from the mesophyll, though a small amount still remained in the 
endodermis and in the transfusion tissue. By January 15 the leaves 
were entirely free from starch with the exception of an occasional 
group of hyaline mesophyll cells, where it was evidently stored. 
Throughout January, February, and early March leaves of a 
number of conifers were collected and examined, but no further 
conclusive evidence of photosynthesis was obtained. Some of the 
species examined retained starch in the mesophyll in greater or less 
abundance throughout the winter, but no increase in quantity, even 
after a comparatively warm bright day, could be .detected micro- 
