INTERDEPENDENCE OF SHOOT AND ROOT 137 
upon the shoot the root system depends for food. Neither 
could survive without the other. Moreover, if either is hindered 
in its development, the other likewise will be stunted. For this 
reason when pots in case of potted plants prevent the further 
development of the root system, the growth of the shoot is checked 
and the plant has to be repotted. Again, the cutting away of the 
roots of a shade tree in excavating for a sewer or sidewalk often 
kills the tree due to diminished water supply. A number of in- 
stances can be cited to show the dependence of the roots upon the 
shoot. For example, it is well known that the roots of Asparagus. 
will not make a good growth unless the shoots are allowed to 
grow during a part of the summer, in order that food may be pro- 
vided for the growth of the roots. Furthermore, it is a common 
practice in eradicating such weeds as Canada Thistle and Quack 
Grass, to starve the underground structures by keeping down the 
shoots. To enable plants to establish a good root system, in 
order that there may be a well developed shoot, is one of the 
chief aims in cultivation. 
The most necessary material absorbed by plants is water, which 
is supplied almost entirely by the roots in higher plants, and 
serves at least a half dozen different purposes. First, water is 
necessary, and in large quantities too, to prevent the shoot from 
becoming dried out through loss of water to the surrounding air. 
Leaves and also stems, unless the latter are well covered with 
bark, are constantly having water evaporated from them and, 
unless this loss is compensated, the shoot will soon die. Second, 
water enables the cells to maintain their turgidity, which main- 
tains the leaves and other soft tissues of the shoot in a rigid posi- 
tion, and thus in a position suitable for work. Third, water is an 
essential constituent of sugar, starch, and other foods made by the 
shoot. Fourth, water as the plant’s solvent is the medium through 
which substances in solution are distributed through the plant. 
Thus through water as a medium, the mineral elements of the soil 
and the foods made in the leaves are carried to all parts of the 
plant. Fifth, it is in the form of a solution in water that sub- 
stances in the plant react chemically with each other. Svzth, 
water is an important constituent of protoplasm, cell walls, and 
other plant structures, usually being more than 90 per cent of 
their fresh weight. Thus it is no wonder that plants must have 
water or they soon perish. 
