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 Hkewise 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. Sixth, 

 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. 



