1914] GATES—XEROPHILY 481 
usually sufficient to satisfy the needs of the plants. In nature, the 
ground, although often frozen to a slight depth, is usually protected 
by a snow cover during the winter (fig. 12). The spaces between 
the snow particles are saturated with water vapor. This produces 
a blanket effect, greatly reducing the temperature changes beneath 
the snow level and tending to keep the temperature nearer the freez- 
ing point in times of cold. Evaporation from the snow also fur- 
nishes an available form of water in winter. 
Frc. 12.—A view in the Mud Lake bog when Chamaedaphne was buried under 80 
cm. of snow; March 26, 1912. 
The evergreen ericads are distinctly grouped apart from the 
deciduous plants. The transpiration of the former in winter was 
2-15 times as great as in the latter. The evergreen habit, even 
with a noteworthy accumulation of recognized xerophytic structures, 
was not as efficient a protection as the deciduous habit. This the 
universal killing of the plants of Chamaedaphne above the snow 
line in the extremely severe winter of 1911-1912 demonstrated, 
while other evergreen plants, not so intensely xeromorphic, but 
entirely covered with snow, were unharmed. 
During the summer the water loss was much greater than in the 
