This section is from "The Horticulturist, And Journal Of Rural Art And Rural Taste", by P. Barry, A. J. Downing, J. Jay Smith, Peter B. Mead, F. W. Woodward, Henry T. Williams. Also available from Amazon: Horticulturist and Journal of Rural Art and Rural Taste.
It is long since we paused from our observations on the science of gardening, but we will now resume (from vol. iii. p. 330) our remarks relative to the roots of plants.
We have seen that plants search after and acquire food by the agency of their roots; and the extremities of these appear to be the chief, if not the only parts employed, in the sucking-in of all food not in a gaseous state, for M. Du-hamel observed that that portion of a soil was soonest exhausted in which the greateet number of the extremities of the roots were assembled. (Physique des Arbres, vol. iii.)
M. M. Senneoier and Carradori found that if roots of the carrot, scorzonera, and radish are placed in water, some with only their extremities immersed, and others with their entire surfaces plunged in, except the extremities, the former imbibe the water rapidly, and the plants continue vegetating; but the others imbibe no perceptible quantity, and speedily wither. It suggests also the reason why the gardener, in applying water or manure to trees or shrubs, does so at a distance from their stems. A good rule for ascertaining the proper distance for such applications, seems to be to make them beneath the circumference of the head of the tree; for, as M.. De Candolle observed, there is usually a relation between that and the length of the roots, so that the rain falling upon the foilage is poured off most abundantly at the distance most desirable for reaching the extremities of the roots.
This explains why the fibrous points of roots are usually annually renewed, and the caudex (or main limb of the root) extended in length: by these means they each year shoot forth into a fresh soil, always changing their direction to where most food is to be obtained. If the extremity of the root is to be cut off, it ceases to increase in length, but enlarges its circle of extension by lateral shoots.
The distance to which the roots of a plant extend is much greater than is usually imagined; and one reason of the stunted growth of plants in a poor soil is, that the sap collected and elaborated by them has to be expended in the extension of the roots, which have to be larger in proportion as the pasturage neat home is height of the wall, and had penetrated the soil at is base.
In deep, poor siliceous soils we have traced the roots of trees from twelve to fourteen feet perpendicular without reaching their termination. Those of the Canada thistle, seven feet; common fern, eight feet; wheat, thirty inches; oats twenty-four inches; potatoes, eighteen inches; onions, twenty inches; carrots, parsnips, and beet, two feet. The distance to which roots will travel, and their tenacity of life, render them often very obnoxious to the gardener. Thus the common couch grass (Triti-cum repens) is the most troublesome of weeds, for every fragment of its far-spreading roots will vegetate- and the sweet-scented coltsfoot and lemon mint are not less to be avoided, for the same cause renders them extremely difficult of extirpation, and they never can be kept within moderate bounds. Yet these creeping rooted plants are not to be condemned without exception; for whoever has grounds under his care bordering upon the sea-shore, the sands of which are troublesomely light and shifting, may have them effectually bound down by inoculating them with slips of the root of these grasses, Elymus arenarius, Carex arenaria. and Arando arenaria.
The roots of plants, unless frozen, are constantly imbibing nourishment, and even developing parts; for if the roots of trees planted during the winter be examined after an interval of a few weeks, they will be found to have emitted fresh raidcles.
It is by their extremities, then, that roots imbibe food; but the orifices of these are so minute, that they can only admit such as is in a state of solution. Carbon reduced to an impalpable powder, being insoluble in water, though offered to the roots of several plants, mingled with that fluid, has never been observed to be absorbed by them; yet it is one of their chief constituents, and is readily absorbed in any combination which renders it fluid.
Roots then must obtain from a soil nourishment to plants in a gaseous or liquid state: we may next, therefore, consider what constituents of soils are capable of being presented in such forms. Water can be the only solvent employed; indeed, so essential is this liquid itself, that no plant can exist where it is entirely absent; and, on the other hand, many will exist with their roots in vessels containing nothing but distilled water. Plants with a broad surface of leaves, as mint, beans, etc, we have always found increase in carbonaceous matter, whilst thus vegetating; but onions, hyacinths, etc, with small surfaces of foliage, we, as invariably, have found to decrease in solid matters. The first, at all times, obtain nourishment by decomposing the carbonic acid gas of the atmosphere: the latter do so in a much smaller proportion: hence the
These observations explain the conflicting statements of Saussure and Hassenfratz on this point: the former experimented with broad, leaved plants; the latter on such as have small foliage. The first maintained that plants increase in solid content when their roots are supplied with water only; the latter denied the fact. - Cottage Gardener,