26 PRACTICAL BOTANY 



\A'ith their roots in the crevices of rocks. It makes a great 

 difference to the plant in what sort of soil it grows. Every 

 good farmer knows that beans will thrive well in a light 

 sundy soil in •\\liich c-orn or broom corn would starve. All 

 wliii <u(^ familiar with tlu^ distribution of our forest trees 

 and shrubs have noticed that some kinds, such as the spruces, 

 most pines, the chestnut, and the jack oak, do well in sandy or 

 other poor soils. On the other hand, the black walnut, the 

 tulip tree, the mulberry, the Osage orange, and the papaw 

 usually flourish only in a deep rich soil. 



27. Direction and extent of the root system. In sand or 

 porous loam the root system of the plant is usually much more 

 extensively developed than in clay. If there is a shallow 

 layer of loam overlying a shaly or clayey subsoil, the roots 

 spread out horizontally but do not go far down in the earth. 

 In sand, roots are usually long and branch but little, A\hile in 

 rich soil they branch so freely as to form a close network. If 

 nutrient materials are irregularly distributed in the earth in 

 which a plant is growuig, rootlets are so much more exten- 

 sively developed in the richer portions of the soil that, as the 

 great agricultural chemist Liebig forcibly said, " R( )ots searel i 

 for food as if they had eyes." The various knids of jilauts 

 ditfcr greatly in the general direction taken by their roots, — 

 those of asparagus, for example, forming a sort of shallow- 

 mat, and those of many hardwood trees, tlu! radish, and the 

 sugar beet beginning with a single taproot -which descends 

 for a considerable distance nearly or quite vertically. 



It is impossible to get an accurate idea of the root system 

 of a very large plant, since its length usually consists maiidy 

 of slender fibers \vhich are inextricably interwoven with each 

 other and penetrate the soil in evcay directicai. The root system 

 even of an oat plant, all contained in a cubic yard or two of 

 soil, has in one instance been found to measure altogether over 

 40(1 feet in length. Many plants ^\•hich ordinarily have their 

 roots near the surface, when grown hi dry soils send theh 

 roots to great depths to secure the needed water supply. lu 



