34 TREES IN WINTER 



while on moist, fertile clay land in the same section such trees 

 are believed to have tap-roots seldom more than six feet long. 



Absorption of water and minerals in solution is the great service 

 of roots, but it is only their smallest branchlets — the root fibrils 

 — that are capable of taking in water. The older parts are soon 

 covered with a waterproof layer of bark and are of service only in 

 conducting fluids to the stem and in holding the tree in place. The 

 fibrils, moreover, do not take in fluids throughout their whole ex- 

 tent but almost exclusively through fine root-hairs, which in the 

 shape of minute tabular cells form a velvety covering on their 

 younger portions (fig. 16). These root-hairs are short-lived, en- 

 during only for a few days or at most weeks. New hairs, however, 

 are constanly being formed toward the root tips as those further 

 back die and shrivel up. In some trees it has been shown that fine 

 threads of various species of moulds growing in the soil surround 

 the root fibrils and take the place of root-hairs, but it still remains 

 true that only the youngest parts of roots are capable of absorbing 

 water. It can be readily understood, therefore, how serious the 

 damage may be to the tree when its almost invisible root fibrils are 

 injured in any way as by transplanting. Fortunately roots can 

 rapidly regenerate lost parts and, if the need of water is lessened 

 by judicious pruning of the crown, the new rootlets formed will be 

 able to absorb enough water to keep the tree from withering. 



How far roots extend from the trunk is not easy to observe. 

 Roots of the Elm have been found clogging up drain pipes 150 feet 

 from the tree, but such a distance must be exceptional. Garden-- 

 ers claim that the parts underground extend laterally as far as 

 those above ground and such a condition would bring the young 

 feeding rootlets directly under the edges of the leafy crown. While 

 this is far from being strictly true, it should be remembered that the 

 absorbing fibrils are in a circle at some distance from the trunk. In 

 consequence, any such treatment of the soil, as adding water or 

 food constituents, should take place at some distance from the 

 trunk rather than at its base, in order to benefit the tree. 



In order to live and grow, roots must have food. This is made 



for them in the leaves and handed down through the stem and 



older roots. If the supply of food is diminished by a partial loss 



of leaves, some of the roots die. If the suj^ply of water and food 



constituents from the soil is lessened by root injuiy a part of the 



leafy crown will die. A rather definite balance exists between the 



extent of the root system and that of the crown. 



PROPERTY Of 

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