THE ROOT
“The stalk or trunk is the upward-growing part of the plant, and needs air and light. The root, on the contrary, is the downward-growing part, and it needs soil and darkness. The extreme ends of the root’s various subdivisions are always growing, always young, of delicate structure, and for that reason admirably fitted for imbibing, very much as a fine sponge would do, the liquids with which the soil is impregnated. Because of their facility in absorbing moisture these ever-growing tip-ends are called spongioles. The spongioles terminate the rootlets, that is to say the final subdivisions of the root, subdivisions known as root-hairs on account of their resemblance to real hair.
“The root takes various forms, which are all reducible to two fundamental types. Sometimes it consists of a main body or tap-root, which sends out branches as it bores deeper into the soil. This designation, tap-root, is a common and familiar term. Sometimes the root assumes the form of a tuft, a bunch of rootlets, simple or branching, which, springing from the same point, continue to grow at a nearly equal rate and on an equal footing as to importance. [[75]]Roots of this sort are commonly known as fibrous roots.
Roots
“As a general rule, the growth of the root keeps pace with that of the stem or trunk. Thus the oak, elm, maple, beech, and all our large trees have a vigorous, deep-growing root as anchorage for the enormous superstructure, to brace it firmly against the wind. But there is no lack of lowly herbage that has roots quite out of proportion to the other parts,—veritable tap-roots of greater size and vigor than many a plant of far greater aërial development can boast. To this class belong the mallow, carrot, and radish. Lucerne has for support to its meager foliage a root that bores two or three meters into the ground.
“An agricultural practice of supreme interest is based, at least partly, on the excessive development of certain roots. The plant is a laboratory where life converts into nutritive matter the manure from [[76]]our stables and poultry-yards. A cart-load of dung becomes at the farmer’s pleasure, after passing through one sort of plant or another, a crop of peas or beans, a basket of fruit, or a loaf of bread. Hence this fertilizer is a very precious thing which nothing can replace and which must be utilized to the very utmost. The nourishment of us all depends on it. Enriched with this fertilizer, the soil produces, we will say, a first harvest of wheat. But wheat with its bunch of short and fine roots, has drawn only upon the upper layer of fertilizing material, leaving intact all that the rain has dissolved and carried down into the lower layers. It has performed its mission admirably, it is true; it has made a clean sweep and converted into wheat all the fertilizer contained in the layer of soil accessible to its roots, so that if wheat were sown a second time no harvest would be obtained. The soil, then, is exhausted on the surface, but in its underlying strata it is still rich. Well, what crop shall we choose for the utilization of these lower strata and the production of still further supplies of food? It cannot be barley, oats, or rye, since their little fibrous roots would find nothing to glean in the surface soil after the first crop of wheat. But it will be lucerne, since this plant will send down its roots, each as thick as your finger, to the depth of one, two, or even three meters, if need be, and give back the fertilizer in the form of forage, which, with the help of the animal that feeds on it, will be converted into nutritious meat, valuable dairy products, excellent wool, or, at the very least, [[77]]animal power for draft service or other work. This succession of two or more different kinds of crops for the utmost utilization of a given area of prepared soil is called rotation of crops, of which there will be more to say later.
“Deep roots, so admirably adapted to the utilization of the lower strata of the soil, become in other circumstances a source of serious difficulty. Suppose a tree is to be transplanted. Its long tap-root will make the operation difficult and hazardous. You must dig deep, both in pulling it out and in replanting it; and then you must be careful not to injure the root, for it is all in one piece and if it does not take hold and grow the sapling will die. In this case it would be much to the tree’s advantage to have fibrous roots running down only to a slight depth; it could then be pulled up easily, and if some roots perished in the operation enough would be left intact to insure the success of the transplanting.
“This result can be obtained: it is no difficult matter to make the tree lose its tap-root and acquire, not a regular bundle of roots of even length; but a short and much ramified root that possesses the advantages of the bunch of small roots without having its shape. Thus in nurseries where young trees remain for some years before being transplanted, after two years’ growth a spade is passed under the surface of the soil to cut off the main root, which would in time become a deep tap-root. The stump that remains then branches out horizontally without going deeper. Another way is to pave the nursery [[78]]bed with tiles. The tap-root of the young tree pushes downward until it reaches this barrier, where it is straightway forced to stop growing in depth and compelled to send out lateral branches.
“The kind of root we have thus far been talking about is primordial, original; every plant has it on emerging from the seed; it appears as soon as the seed germinates. But many plants have other roots that develop at different points of the stem, replacing the original root when that dies, or at least coming to its aid if it continues to live. They are called adventitious roots, and they play a highly important part, notably in certain horticultural operations such as propagating by slips and layers, which we will talk about later.