86 BOTANICAL GAZETTE [ FEBRUARY 
The experiment was repeated with an Alisma leaf on bulb B 
and the damp block of plaster on R. When the temperature 
fell, the leaf, in spite of its smaller volume, cooled more slowly 
than the plaster; there was therefore a relative warming of the 
leaf lasting about 15 minutes, and the reverse effect occurred as 
ENE. 
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Fic. 3.—See Experiment 46, p. 85. 
the air became warmer again on the door and windows being 
closed. 
These experiments show clearly the necessity of using for the 
control bulb a body equaling in volume and conductivity that on 
the experimental bulb. A cut leaf with closed stomata answers 
this purpose well enough. 
Another element of some importance is the condition of the 
air. It is obvious that, if the air becomes drier, the evaporation 
from the experimental leaf will increase, and the curve might be 
