454 BOTANICAL GAZETTE [JUNE 
surface position of the leaves during winter is really a xerophytic 
modification, reducing the amount of radiant energy absorbed at 
a time when it would be needlessly dissipated in increase of water 
loss, which the absence of phytosynthesis and the closure of the 
stomates does not occasion. Leaves which develop upon Chamae- 
daphne in the Larix association are much less xerophytically modi- 
fied. They are much more subject to winter killing. 
The loss of water by the leaves exercises a twofold function. 
The excess of radiant energy absorbed and not used in photosyn- 
thesis could easily raise the temperature of the leaf to the death 
‘point during hot waves, were it not dissipated in vaporizing water. 
Darwin (13), through the use of a resistance thermometer, demon- 
strated that, with the check to transpiration that comes with 
induced closure of the stomates, the temperature of the leaf rises. 
Normally this higher temperature would not occur, for the excess of 
radiant energy being used to vaporize water causes a lowering of 
temperature. The loss of water in the leaves maintains a stream 
of water from the roots up. This is necessary for the removal of 
the products of respiration (BABcocK 1) and for the lifting of the 
absorbed mineral material to the leaves. Water is also necessary 
in photosynthesis. 
As Livincston (30) puts it: ‘‘The total amount of tran- 
spirational water lost from a plant, for any given period, may be 
considered as a summation of the effects of the evaporating power 
of the air and of the radiant energy absorbed throughout the period, 
modified by certain secondary effects of these conditions and certain 
responses to other conditions.’’ The ratio of the water income to 
that of the removal must not fall below unity for any considerable 
time in plants which are not water-storing. Quoting again from 
LIvINGSTON (31): “The really crucial question with regard to any 
soil . is... . at what rate, and for how long a time, can it 
deiner wale to a unit area of a water-absorbing surface?” That 
water is supplied in sufficient quantities during the most extreme 
conditions of summer that obtain in nature in this region is evident 
from this investigation. The opposite statement is true for winter, 
namely, that in very severe winters the removal of water from the 
exposed parts of certain plants is so in excess of the supply that too 
