. Cyclopedia of farm crops. Farm produce; Agriculture. Fig. 25. Four steps in process of cell-division. Mother-cell .it left, fill" advanced in divison; daughter-cell at right. which, the tap-root (Fig. 26), goes deep into the soil, growing straight down and sending out lateral roots at intervals. The other spreads out near the surface of the soil (Fig. 27) and consists of a mass of fine rootlets. It has the advantage of estab- lishing itself quickly and absorbing moisture vigor- ously from the start, thus inducing a rapid growth of the plant. But it cannot utilize the deeper soil food no
. Cyclopedia of farm crops. Farm produce; Agriculture. Fig. 25. Four steps in process of cell-division. Mother-cell .it left, fill" advanced in divison; daughter-cell at right. which, the tap-root (Fig. 26), goes deep into the soil, growing straight down and sending out lateral roots at intervals. The other spreads out near the surface of the soil (Fig. 27) and consists of a mass of fine rootlets. It has the advantage of estab- lishing itself quickly and absorbing moisture vigor- ously from the start, thus inducing a rapid growth of the plant. But it cannot utilize the deeper soil food nor withstand drought. On the other hand, tap-roots many endure long periods of drought: the long-rooted Peruvian cotton is said to survive a rainless period of six years. A well-developed root system forms a mass of finely interlacing filaments that thoroughly ex- plore the soil. The total length of these has been estimated at a quarter of a mile for a vigorous corn plant, while measurements on a squash vine proved the rootto be over fifteen miles in length, uj}&^-^.. Fig. 26. Tap-root. Dandelion. the greater part of this being produced at the rate of a thousand feet per day. Because of need of air, most roots are unable to thrive in wet soil, and their best work is done in soil in which the water is held in a thin film around the soil-particles. Each particle constitutes a minute water reservoir. To reach and tap these reservoirs is the work of the root-hairs, which ap- pear just back of the root-tip as outgrowths from the surface cells of the root (Figs. 28 and 29). They force themselves energetically between the soil-particles and attach themselves so closely that they often break oif rather than loosen their hold when the root is pulled up. Thus they come into contact with the water-films that surround the particles, and by means of water-attracting sub- stances within the root-hair they pull the water away from the particles. As each tiny reservoir is emptied of its sup
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