The Vegetable World: Being a History of Plants, with Their Botanical Descriptions and Peculiar Properties

The multiplication of roots takes place, sometimes by their elongation and thickening, as in the Carrot, Turnip, and Beet (Fig. 6). When short and slender, natural rootlets, named radicles, are emitted, or rootlets which accompany the descending body; this is the tap-root. Sometimes the root is entirely composed of axils, more or less numerous, and nearly of the same size, which unite at the col/um, or point of juncture, of the stem and

root, of which the Melon (Fig. 7), fasciculated This is thecaudex. examples. the Lily, and the Palms arethe Wheat-plant,

Fig. 6.—Tap-root of the Beet. Fig. 7.—Fasciculated root of Melon.

This difference in the structure and constitution of the root must be taken into consideration under a great number of circumstances. The old Fir-tree firmly anchored in the ground by its deep and spreading roots, braves the most violent storms, and even on the mountain-top resists the most terrible tempests. But the Fan-palm, whose fasciculated roots, spread themselves horizontally in the sand, is overthrown, beaten down by the wind, when it has reached the height of five or six feet. If the stem of this palm be artificially supported, it may attain, even in our climate, to a height of fifty or sixty feet. In front of the great amphitheatre in the Museum of Natural History at Paris, two Fan-palms thus

6

THE VEGETABLE WORLD.

supported rear their lofty heads, charged with their fan-like tuft of leaves (Fig. 8).

Some acquaintance with the form of roots will soon find its practical uses. In watering a plant, it is necessary to pour in the water at the foot of the stem, if it is tap-rooted; on the contrary, if the root is fasciculated, it should be poured out at some distance from the stem, in order that the spreading roots may receive the benefit of the water. In the cultivation of plants we manure the surface of the soil, or of the deeper beds, according as the plant has tap roots or fasciculated roots. In scientific farming a plant with fasciculated roots which exhausts the soil on the surface, is succeeded by a plant with a tap root, which seeks it nourishment at a greater depth in the soil.

Fig. 8.—Fan-palm at the entrance of the Amphitheatre at the Jardin des Plantes.

This diversity in the structure of roots is not the work of chance,

but the result of design. The composition of the soil varies singularly in different parts of the globe. In order that every point of the surface of the earth should be covered with vegeta-incomparabletion, and that no part of it should be without that adornment, roots must take very. varying shapes in order to themselves to these varieties in the composition ofaccommodate the soil. In one place the soil is hard and stony, heavy or light, formed of sand or clay; in another it is dry or moist; elsewhere it is exposed to the heat of a burning sun, or swept, on the heights, currents; sometimesby the violence of the winds and atmospheric it is sheltered from these movements of the wind in the depth of some warm valley. Roots, hard and woody, separated into strong yet finely divided at their terminations, are requisiteramifications, for mountain plants, whose roots are to live in the midst of rocks or between the stones, in order that they may penetrate between the chinks of the rocks, and cling to them with sufficient force to resist the violence of hurricanes and other aerial tempests. Straight tap-roots and slightly branching plants are fit for light and permeable soils. They would not suit close, clayey, and shallow soils. Such districts are suitable for plants whose roots stand horizontally just under the surface of the soil.

These considerations are of great importance to the cultivator, who, if he would propagate plants successfully, must carefully study the nature of the soil, and choose for his experiments plants having roots adapted to it.

Two modifications may be found in the two classes of roots of which we have been speaking. It sometimes happens that these roots form themselves into masses more or less voluminous, full of nutritive matter, which is destined to nourish the plant or to favour its increase. Common examples of this structure are presented to us by the Orchis mascula of our meadows and woods, the Anemone, Ranunculus, and Dahlia of our flower gardens. These roots are called tuberous when they take the form of the roots of the Dahlia (Fig. 9), or tubero-fibrous when they take the form of those of the Orchis (Fig. 10).

These enlargements of the root have a special use in the life of the plant. It is their function to accumulate, in the lower part of the vegetable, supplies of nutritive matter, consisting chiefly

of fécula, whose purpose is to aid in the development of the plant during a certain period of its existence. Plants derive their principal nourishment from their roots. We should then naturally be led to think that the bulk of the

Fig. 9,—Tuberons root of the Dahlia. Fig. 10.--Tubero-fibrous root of Orchis masculata,

roots would be always in proportion to the size of the stem and branches of a plant. This is generally true for the same species; we know, for instance, that the more numerous the branches of an Oak are, the more abundant are its roots; more than this, it is known that the strongest roots in the oak correspond with its strongest branches. But if we turn from one species of plant to another, we find, not without surprise, that the roots of the palms and pines bear little proportion to their height; whilst some plants, such as Lucerne, Bryony, and Ononis (Cammock), are provided with enormous roots in proportion to the small dimensions of their stems. : If roots do not show in their rarifonticns the same regular and _ unvarying arrangement that we see in leaves and boughs, the cause

is not difficult to understand. In the bosom of the earth they meet with obstacles which leaves and branches never meet with in the air. The latter consequently spread freely in every direction, whilst roots are incessantly stopped by all sorts of obstacles. They are constantly cramped in their lengthening or thickening, and are forced to turn aside from the course which they ought naturally to follow, and obliged to twist round to surmount the impediments opposed to them by the unequal hardness of the soil, the presence of walls, rocks, or of other roots. From these causes arise the deformities which we notice in their outward structure, and the numerous windings observable in their branches.

The manner in which roots succeed in overcoming obstacles has always been a subject of surprise to the observer. The roots of trees and shrubs, when cramped or hindered in their progress, have been observed to exhibit considerable mechanical force, throwing down walls or splitting rocks; and in other cases clinging together in bunches, or spreading out their fibres over a prodigious space, in order to follow the course of a rivulet with its friendly moisture. Who has not seen with admiration how roots will adapt themselves to the special circumstances of the soil, dividing their filaments in a soil fit for them almost to infinity, - elsewhere abandoning a sterile soil to seek one farther off, which is favourable to them; and as the ground was more or less hard, wet or dry, heavy or light, sandy or stony, varying their shapes accordingly? We are compelled to acknowledge that there is in these selections made by roots a true manifestation of vital instinct. Duhamel, a botanist of the last century, relates, that, wishing to preserve a field of rich soil from the roots of a row of elms which would soon have exhausted it, he had a ditch dug between the field and the trees, in order to cut the roots off from it. But he saw, with surprise, that those roots which had not been severed in the operation had made their way down the slope so as to avoid meeting the light, had passed under the ditch, and were again spreading themselves over the field. It was in reference to an occurrence of this kind that Bonnet, the Swiss naturalist, said that it was sometimes difficult to distinguish “a cat from a rose tree;” a quaint, if not a witty remark.

Hitherto we have occupied ourselves in considering the roots constituting the descending and normal system of vegetation. There are, f , however, some roots which are developed along the stem itself. Organs, supplementary in some sort, they come as helps to the roots properly so called, and replace them when by any cause they have been destroyed. Inthe Wheat-plant, the Dog’s-grass (Fig. 11), and in general in all plants of the grass family, the lower part of the stem gives rise to supplementary roots, to which these common field plants owe a portion of their vigour and their resistance to the causes which would destroy them (Fig. 11). In the Primrose (Primula) both the === principal and the

Fig. 11.—Adventitions roots of the Couch-grass, Agropyrum repens, =. secondary —_roots which spring from it perish after some years of growth. But the adventitious roots (Fig. 12) springing from the lower part of the stalk prevent the plant from dying. In the tropical forests of America and Asia, the Vanilla, whose

fruit is so sought after for its sweet aroma, twines its slender stem round the neighbouring trees, forming an elegant, flexible, and aerial garland, at once a grateful and pleasing ornament in these — vast solitudes. The underground roots of the vanilla would not be sufficient for the nutriment of the plant, and the rising of the nourishing sap would take place too slowly. But nature has provided for this inconvenience by the adventitious roots which the plant throws out at intervals along its stem. Living in the warm and humid atmosphere of tropical forests, the stronger shoots soon reach the ground, and root themselves in the soil. Others float freely in the atmosphere, inhaling the humidity and conveying it to the parent stem. All these processes may be observed in full operation in many well-ordered conservatories.

A grand tree, the Pagoda Fig-tree (Ficus religiosa), adorns the landscape of India, and presents the most remarkable development of adventitious roots. When the parent stem has attained the height of some fifty or sixty fect, it throws out its lateral branches in every direction, and each branch in its turn throws _

dut adventitious roots, which descend perpendicularly in long

rs a

Fig. 13,—Conservatory of the Jardin des Plantes, Paris, with the climbing roots of the Vanilla. slender shoots till they reach the ground. When they have rooted themselves in the soil, they increase rapidly in diameter, and soon