Students' handbook to accompany Plants and their uses . upply. In parts of California it has been foundthat common farm plants, such as alfalfa and wheat, may haveroots reaching moist earth at a depth of from 13 to 15 feet. Why is deep plowing between hills of half-grown cornlikely to injure the crop ? 23. Pull of roots due to shortening. Frequently rootlets orthe taproots of herbaceous plants shorten after they are fullygrown. This shortening has a tendency to pull the stem andleaves of the plant downward. It is interesting to notice howsome plants with rosettes of leaves, like chicory, dande
Students' handbook to accompany Plants and their uses . upply. In parts of California it has been foundthat common farm plants, such as alfalfa and wheat, may haveroots reaching moist earth at a depth of from 13 to 15 feet. Why is deep plowing between hills of half-grown cornlikely to injure the crop ? 23. Pull of roots due to shortening. Frequently rootlets orthe taproots of herbaceous plants shorten after they are fullygrown. This shortening has a tendency to pull the stem andleaves of the plant downward. It is interesting to notice howsome plants with rosettes of leaves, like chicory, dandelion, 2G INTRODUCTION TO BOTANY ami full dandelion, pull tlieir rosettes down tightly against thesurface of a lawn, kill the surrounding grass, and thus securefor themselves a little elear space in which to grow. 24. Effects of roots on the soil. If we dig up a spadeful ofearth from a well-grassed meadow or from a little inside thecircumference of the circle formed by the roots of a tree, weshaH find the soil bound together by the living roots or full. is. Cyinvss trees (Taxudiiun) growing in a swamp The conical knees jjrowin;; from the routs ami nearly always above water arethought to serve as channels to supply air to the rods of little, crooked, tubular channels left by the decay of deadones. Thus the soil is in the one case held together so as toprevent, its becoming gullied and washed away by rains, and inthe other case made more porous and more easily penetratedby air and water. The latter effect is a very important one inthe case of stiff day soils, which, when closely packed, arealmost, waterproof. The extensive washing away of soils when they are unpro-tected by a covering of plants, such as grass, shrubs, or forest ROOTS AND THEIR RELATION TO PLANTS 27 growth, is one of the most serious calamities that can befall acountry. It is especially formidable in hilly regions, winchmay become wholly uninhabitable if the forests are cut offand the turf on the hillsides is
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