26 PRACTICAL BOTANY 



with 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 

 sandy soil in which corn or broom corn would starve. All 

 who are familiar with the 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 nourish 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, while 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 growing, rootlets are so much more exten- 

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

 great agricultural chemist Liebig forcibly said, " Roots search 

 for food as if they had eyes." The various kinds of plants 

 differ .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, the 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 mainly 

 of slender fibers which are inextricably interwoven with each 

 other and penetrate the soil in every direction. 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 

 450 feet in length. Many plants which ordinarily have their 

 roots near the surface, when grown in dry soils send their 

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



