482 BOTANICAL GAZETTE [JUNE 
winter, especially, to be sure, in plants of the deciduous habit. 
Transpiration bore a rather definite relation to the evaporating 
power of the air. This relation varied both with species and with 
individuals. Its numerical value was from one-third to one- 
twelfth that of the air. It was obvious how efficient the xero- 
morphic structure of the evergreen trees and shrubs is in lowering 
the rate of transpiration during the summer. During the winter 
the absolute value of transpiration of Chamaedaphne varied up to 
0.02 gm. per hour per too sq. cm. of leaf surface as a maximum 
under outdoor conditions, and 0.07 gm. under indoor conditions, 
and did not exceed 0. 30 gm. under conditions above a hot radiator, 
which were severer than ever experienced in nature. Transpiration 
from distilled water was 1.09 times that from bog water. - During 
the summer the normal rate at night is less than 0.10 gm., while 
in the daytime it approaches 0.80 gm. Only on extremely hot 
days with low relative humidity did the rate exceed 1.00 gm. 
The maximum recorded was 1.70 gm./hr./1oo sq.cm. This means 
that the average summer rate of transpiration in Chamaedaphne 
calyculata is 25-30 times greater than the maximum winter rate, 
while the maximum summer rate was over 80 times that of the 
maximum winter rate. For deciduous plants the difference is very 
much greater. 
The highest rates of water loss were in the more hydrophytic 
plants, Nymphaea advena, Sagittaria latifolia, and Carex filiformis, 
which agrees with the experimental data obtained by Oris (36) by 
a different method. In a potted plant of Sagittaria the maximum 
rate obtained during the investigation occurred on the afternoon of 
July 5, 1912 (4.82 gm./hr./1oo sq. cm.). 
As has been stated above and is here briefly repeated, during 
the winter the transpiration and rate of conduction of water are 
much higher in the evergreen plants (Chamaedaphne calyculata, 
Andromeda glaucophylla, Vaccinium macrocarpon, and Picea 
mariana) than in the deciduous ones. In the summer the rate of 
transpiration and conduction in the herbaceous plants (Nymphaea 
advena, Sagittaria latifolia, Eupatorium perfoliatum, Asclepias 
incarnata, Dulichium arundinaceum, Aspidium thelypteris, Hyperi- 
cum virginicum, Carex filiformis, Cicuta maculata, and Potentilla 
