THE WORK OF ROOTS
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&c.). In addition to this it has to assimilate or incorporate the latter into its fabric, i.e. to transform the organic foodstuffs which it manufactures into plant substance, just as a dog converts meat and biscuit into dog substance.
   The organs concerned in these processes are the root and shoot systems, which are normally unfolded in the soil and in the air, respectively. Typically the root is an aggregate of slender filaments developed beneath the surface of the ground and bearing a closely-aggregated pile of minute tubules — extensions of the superficial cells—known as the root hairs. These roots, with' their root hairs, occupy the interstices between the soil particles, and through their agency the water and dissolved salts of the soil gain entrance into the plant body.
   The root system may consist of a principal root, which penetrates the ground, together with lateral roots, and yet other branches of the third degree. As a plant increases in age this primary root system is commonly supplemented by additional roots which arise directly from the stem, whilst in perennial plants, especially such as possess creeping underground stems, the whole of the roots will belong to this latter class.
   Actually the root is a most extensive absorbent surface adapted to occupy the interstices of the soil, and to obtain therefrom the water and dissolved salts which clothe the surfaces of the soil particles. How extensive is the root system, and how thorough its exploration of the soil will be appreciated From the following example. (See also Plate III.) In a field )f maize the roots occupy entirely the whole upper 3 feet of the ield, and attain a density such that nowhere is a cubic inch )f soil to be found not penetrated and explored by a rootlet.
   An index of the work done by the root in water absorption s obtained from the fact that it has been ascertained that maize ranspires (i.e. evaporates into the air) on the average 2.9 lb. er stalk per diem. This means that the crop planted in the rdinary way would take 244 tons of water from an acre of round during the growing season, and this from a soil so ry that no mere pressure could express a drop of water from it.
 This root system occupies and adjusts itself to the interstices f the soil, i.e. spaces filled with moisture-saturated air in