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cation of their favourite process, in the general cultivation of land, are undoubted.
Van Helmont's ideas, that all the products of vegetables were capable of being generated by water alone, are not strictly just ; but it is certain, that without water, vegetables cannot grow; and indeed, that their growth is regulated, if not entirely dependant upon the supply of water to the Roots.
Jethro Tull's opinion, that the native soil in itself contains all that is necessary for the sustenance of vegetables, is refuted by every year's experience of the gardener and farmer; but his method and principle of cultivation will always be found to increase fertility; and Mr. Curwen’s conclusions, that the vapours arising from the soil, when stirred up, affords additional sustenance to Plants, by being absorbed and taken into the system by the leaves, is equally fallacious; for if such be the case, the vapour arising from the earth, being so light as to be wafted by the most gentle current of air, those vegetables growing on the land, which is lying alongside that which is hoed or stirred
up, must be benefited; but this is not found to be so; still the operation is undoubtedly beneficial.
The true principles upon which the whole is sustained appear to be the following:
Water holding, in solution certain substances furnishes the sole Food of Plants.
The Roots of Plants having extracted and consumed that part of water which is adapted to their
purpose, the residue becomes useless and obnoxious, and, unless removed, engenders disease.
Therefore, to keep up a constant and regular supply of food, and to preserve health, a change or circulation of water is as necessary to vegetables as a circulation or change of air is to animals.
Earth by itself (as subjected to the influence of cultivation) is in no other respect requisite for the sustenance of Plants than as a laboratory, and bed or couch, to prepare the food, and for the roots to range, feed, and repose in. .
Earth of every kind is capable of holding a certain portion of water by capillary attraction, and, according to its texture, of admitting a rapid or slow passage of water through it.
The gravity of water falling on the surface of the earth, in rain or otherwise, occasions its descending motion or filtration, and when the surface is heated by the sun, the water there is rarified, raised again, and passed off in vapour : and thus the attraction being increased, an ascending motion is created.
Water, in its ascent and descent, being brought in contact with the carbonaceous matter contained in the earth, dissolves a portion, and is thereby replenished with the food required for the sustenance of vegetables, and thus passing among the roots it is distributed.
It is demonstrated by analysis, that the most fertile soils are those, which are so compounded, as to admit of the greatest, most minute, and most
immediate division, expansion, and dissemination
And, consequently, the most effectual modes of
This is the true cause of the benefits resulting from the horse-hoeing of Tull and Mr. Curwen.
The more perfectly divided the soil, the more perfect and uniform will be the ascent and descentof the moisture; and the more miņutely divided and disseminated, the carbonaceous or grand principle of fertility, the more readily dissolved and incor, porated will it be with the water, and the more perfectly prepared and brought within reach of the Roots of Plants.
It may further be observed, that upon those principles rest the beneficial results of the agri. cultural processes of draining, irrigation, calcareous dressings, keeping the surface clear from weeds, and properly exposing it to the action of the sun, the air, &c.
From the preceding observations, we must also conclude, that not only the composition of the bed or couch requires particular attention, but that the nature of the substrata on which it rests, is also very material and important: for if this be so constituted and formed, as to retain the superfluous water, and occasion it to stagnate about the roots,
it will produce sterility, disease, and death ; and if it be too open and dry, it will, by permitting the water to drain off too rapidly, and by its incapacity to return it, rob the soil of its carbonaceous principle, and render it sterile.
No doubt, with vegetables as with animals, the quantity and quality of the food, and the protection and support afforded, determine their capacity and produce; therefore, in the course of cultivation, all arrangements must be made to accord with the object in view ; and in this, our desires must conform to our means : it will be wasteful folly to provide a bed or couch, and food sufficient for a large tree, when we have space or room only for the trunk, branches, &c. of a small one, and the reverse.
Upon what principles, and by what application of
Many describe the Sap in vegetables as circulat-
Bradley says, “ The many curious observations which have been made concerning the structure of animal bodies, and what Dr. Grew, Malpigius, and myself have remarked, in the structure of vegetables, may ascertain to us that life, whether it be animal or vegetable, must be maintained by a due circulation and distribution of juices in the bodies they are to support."
And proceeds to explain his opinion, “ That the Sap circulates in