20 6 
Tuttle . — Induced Changes in Reserve 
The increase in the starch content of these leaves is much more evident 
than the decrease in the oils and fats which one would suppose must be 
taking place, as that seems the only source from which the starch can be 
derived, for the factor of photosynthesis has been eliminated by placing the 
material in darkness. All the leaves showing a large amount of starch 
gave a strong reaction with the test for oils and fats. In horizontal sections 
passing through the epidermis there seems to be quite as much oil as starch 
present. The palisade tissue shows no appreciable decrease. It is only in the 
cells of the mesophyll that an actual difference has been recognized. Here 
the decrease is quite evident, as will be seen by comparing Figs. 5 and 6 . 
Fig. 5 . Cross-section of Linnaea leaf, showing Fig. 6. Cross-section of Linnaea leaf, show- 
fats and oils before exposure to higher temperature. ing decreased fat and oil content. Material ex- 
Section treated with i per cent, osmic acid. posed to higher temperature for one week. Sec- 
tion treated with i per cent, osmic acid. 
III. Reconversion of Starch into Fats and Oils. 
Having shown that starch appears in those leaves subjected to a higher 
temperature, it was then attempted to cause a reconversion of the starch to 
oils and fats by lowering the temperature. Material of Linnaea which had 
been kept at 68° F. (20° C.) for a week, and which showed as a result a high 
starch content, was placed outside in darkness on two different dates — 
November 25 and December 13. As will be seen from Tables III and IV, 
the temperature conditions were very different during the two experiments. 
Table III. 
Material containing Starch exposed to moderately low Temperature . 
Date . 
Av. 
Temperature. 
Experiment. 
Control. 
Nov. 25 
2 5° F. (— 3 0 C.) 
Strong starch reaction 
Strong starch reaction 
„ 30 
36 F. (2 0 C.) 
Decreased starch content, four 
00 07 
leaves out of six destarchified 
Dec. 4 
28° F. (- 2°C.) 
All material destarchified 
09 01 
