268 LEAVES 
summer drought and thereby decrease their transpiring surface. 
Of course this is not a protection to the leaves but to the plant. 
Most trees of the temperate region shed all their leaves in autumn. 
Such trees are known as deciduous. This shedding of leaves in 
autumn protects the plant against transpiration during winter. 
Even with leaves absent, trees are sometimes killed by trans- 
piration from buds and twigs. The killing by transpiration in 
winter is not due to a great water loss, but to the inability of the 
roots to furnish water to compensate for the loss. Since the roots 
of most trees are not far below the surface, a deep freeze may 
freeze the water about them. Even when the soil is cold, roots 
take up water slowly, and when the water is frozen into ice, they 
can not absorb it at all. With only a little water furnished by 
the roots, a small amount of transpiration may be sufficient to 
cause the death of the cells in the buds and twigs. 
In transplanting trees, it is usually necessary to prune the top, 
because the root system has been partly broken and cut away, 
and consequently is not able to furnish enough water to compen- 
sate for the amount transpired from a shoot of normal size. 
Pruning the top results in fewer leaves and hence less transpiring 
surface. Even after trees have been transplanted and well 
established, a reduction of the transpiring surface by pruning the 
top is often helpful, but usually the pruning of such trees has 
other purposes as pointed out in the study of buds. However, 
since the leaves are food-making organs, only a limited number 
of them can be removed or the plant will suffer from starvation. 
Supplying moisture to the soil protects against injuries result- 
ing from transpiration. Plants in the greenhouse must have the 
soil about their roots kept moist by watering. In the dry 
western regions water is supplied to the soil by methods of 
irrigation. 
Much can be done in protecting against transpiration by 
conserving the moisture of the soil. If an orchard is in sod, 
many tons of water will be lost from the soil through the trans- 
piration of the grass. By plowing and keeping the ground free 
from grass and weeds, the water of the soil is conserved for the 
fruit trees. In regions where dry farming is practiced, the 
ground is fallowed during one year and then seeded the second 
year. Fallowing consists in keeping the ground plowed and well 
harrowed, so that the surface will be covered with a mulch and 
