174 DRY-FARMING 
is drawn from the soil by the roots through the stems 
is evaporated into the air. There is some evapora- 
tion of water from the stems and branches of plants, 
but it is seldom more than a thirtieth or a fortieth of 
the total transpiration. The evaporation of water 
from the leaves through the breathing-pores is the 
so-called transpiration, which is the greatest cause 
of the loss of soil-water under dry-farm conditions. 
It is to the prevention of this transpiration that 
much investigation must be given by future students 
of dry-farming. 
Transpiration 
As water evaporates through the breathing-pores 
from the leaves it necessarily follows that a demand 
is made upon the lower portions of the plant for 
more water. ‘The effect of the loss of water is felt 
throughout the whole plant and is, undoubtedly, one 
of the chief causes of the absorption of water from 
the soil. As evaporation is diminished the amount 
of water that enters the plants is also diminished. 
Yet transpiration appears to be a process wholly 
necessary for plant life. The question is, simply, 
to what extent it may be diminished without injuring 
plant growth. Many students believe that the car- 
bon assimilation of the plant, which is fundamentally 
important in plant growth, cannot be continued un- 
less there is a steady stream of water passing through 
the plant and then evaporating from the leaves. 
