186 PRACTICAL COURSE IN BOTANY 
moisture, by means of grooves, channels, and taper-pointed 
leaves, which act as natural gutters and drain pipes. 
203. The fall of the leaf. — This is, in effect, an adjust- 
ment to change of temperature, but that it is not directly due 
to cold is shown by Exp. 75, and also by the fact that leaves 
in the tropics and those of evergreens, while they do not fall 
at stated periods like the bulk of the foliage in the temperate 
zones, are cut off just the same and replaced by new ones, 
whenever, for any 
reason, they are un- 
able to perform their 
function. In cold 
climates they fall at 
the approach of 
winter, not because 
the frost loosens 
them, but because 
the roots arenot able 
to absorb enough 
moisture to supply 
them with material 
for making food. 
The needles and the 
Fic. 254. — Fallen leaves. Notice how they cover scale-leaves charac- 
the ground with a warm mulch, protecting the soil saty 
from denudation, and the roots and seeds from frost teristic of evenoreene 
in cold regions are 
enabled to persist indefinitely by reason of their contracted 
surface. This prevents the dissipation of moisture and affords 
no lodging for the accumulations of sleet and snow that 
would otherwise cumber and perhaps break the boughs with 
their weight. Trees and shrubs that shed their leaves in win- 
ter are said to be deciduous, from a Latin word meaning “to 
fall.” Can you mention some advantages of the deciduous 
habit to a plant with broad, expanded leaves, growing in 
a cold climate? 
The mechanical means by which the leaf fall is accom- 
