Roots. The root not only supports the plant by fixing it in the soil, but affords a channel for the conveyance of nourishment.
the extremity of each fibre of a root, there is an expansion of the cellular integument, called spongiole, from its resemblance to a small sponge; being full of pores, it absorbs the water from the soil. There are pores in every part of a plant, above ground, but they are almost wholly for the purpose of exhalation. The roots have no pores, except in the spongioles at the extremities. It would be useless for them to be furnished with evaporating pores, since they are not exposed to the atmosphere, where alone evaporation could take place. The tendrils of vines, and of other climb' ing plants, which serve to fix them against a wall, or the trunk of a tree, cannot be considered as roots; since, though they answer the purpose of sustaining the plant, they are unable to supply it with nourishment. But there arc some parasitical plants, such as the mistletoe, which, having no immediate communication with the earth, strike their fibres into the stems or branches of a tree, and derive their nourishment from this richly-prepared soil: yet, as the absorption in this case is not carried on by the regular mode of spongioles, their fibres are not denominated roots. The spongioles act only by capillary attraction and suck up moisture, just as a lump of sugar absorbs the water into which it is dipped. As a proof of this it has been shown, that if roots, saturated with moisture, be transplanted into very dry earth, the latter will absorb the moisture from the roots. Absorption does not immediately cease upon the death of a plant, as the blood ceases to circulate upon the expiration of animal life; but when the vessels, through which the fluid should pass, have lost their vital energy, that susceptibility of irritation and contraction, which enabled them to propel the fluid upward, ceases, and it can no longer ascend into the roots, but remains stagnant in the spongioles, which soon become satu-rated. Disease and putrefaction follow; and that nourishment which was designed to sustain life now serves only to accelerate disorganisation. The fluid is, however, still performing the part assigned to it by the Creator, for it it be necessary to supply living plants with food, it is also necessary to destroy those which have censed to live, in order that the earth may not be encumbered with bodies become useless, and that their disorganized particles may contribute to the growth of living plants. Thus, the putrefaction of leaves, straw, etc, which reduces the bodies to their simple elements, prepares them to become once more component parts of living plants. Botanists distinguish several kinds of roots. The radix fibrosa, or fibrous root, is the most common in its form: it consists of a collection or bundle of fibres. The roots of many grasses, and most annual herbs, are of this description. The couch-grass is an example of the radix repens, or creeping-root. If an attempt be made to eradicate such roots, a succession of bunches of fibres are met with, springing from an apparent root which grows horizontally, and appears to be endless. This long horizontal fibre is, however, not a root, but a subterraneous branch, for it has no spongioles. the real roots are the small bundle of fibres which spring from it. Such. a root is very tenacious of life, as any portion in which there is an articulation will grow. The ox-eye, whose strong penetrating roots strike deep into the earth, furnishes an example of the radix fusiformis, or spindle-shaped. It is also called the tap-root, from its tapering so considerably towards the end. The radix bu/bosa, or bulbous-root, such as that of the lily, the hyacinth, or the onion, is improperly so called, for the tufts of fibres, pendant from the bulb, are the roots. The bulb constitutes the stem of the plant. The potato belongs to the class of tuberous, or knotted roots, which are of various kinds, comprehending all such as have fleshy knobs, or tumours. In all cases they are to be considered as reservoirs of nourishment, which enable the plant to sustain the casual privations of a barren or dry soil. The root of the orchis is deserving of notice, from its singularity. It consists of two lobes, somewhat similar to the two parts into which a bean is divided. One of these perishes every year, and another shoots up on the opposite side of the remaining lobe. The stem rises every spring from between the two lobes, and since the new lobe does not occupy the same place as its predecessor, the orchis every year moves a little onwards The duration of roots is either annual, biennial, or perennial. To the first belong plants the existence of which is limited to one season, such as barley, and a vast number of garden and field flowers. The biennial root produces, the first season, only herbage, and the following summer, flowers and fruits, or seed; after which it perishes. To the perennial belong plants which live to an indefinite period, such as trees and shrubs. (See Stems and Leaves, p. 210).