Since the grosser Vegetable Particles, when they have pass’d thro’ a Plant, together with their moist Vehicle, do fly up into the Air invisibly; ’tis not likely they should, in the Earth, fall off from the Superficies of the Pores, by their own Gravity: And if they did fall off, they might fly away as easily before they enter’d Plants, as they do after they have pass’d thro’ them; and then a Soil might become the poorer[14] for all the Culture and Stirring we bestow upon it; tho’ no Plants were in it; contrary to Experience.
[14]But we see it is always the richer by being frequently turned and exposed to the Atmosphere: Therefore Plants must take all their Pabulum from a Superficies of Parts of Earth; except what may perhaps be contained in Water fine enough to enter Roots intire with the Water.
It must be own’d, that Water does ever carry, in its Interstices, Particles of Earth fine enough to enter Roots; because I have seen, that a great Quantity of Earth (in my Experiments) will pass out of Roots set in Rain-water; and tis found that Water can never be, by any Art, wholly freed from its earthy Charge; therefore it must have carry’d in some Particles of Earth along with it: But yet I cannot hence conclude, that the Water did first take these fine Particles from the aforesaid Superficies: I rather think, that they are exhal’d, together with very small Pieces to which they adhere, and in the Vapour divided by the Aereal Nitre; and, when the Vapour is condens’d, they descend with it to replenish the Pasture of Plants; and that these do not enter intire into Roots, neither does any other of the earthy Charge that any Water contains; except such fine Particles which have already pass’d thro’ the Vegetable Vessels, and been thence exhal’d.
This Conjecture is the more probable, for that Rain-Water is as nourishing to Plants set therein as Spring-Water, tho’ the latter have more Earth in it; and tho’ Spring-water have some Particles in it that will enter intire into Roots, yet we must consider, that even that Water may have been many times exhal’d into the Air, and may have still retain’d a great Quantity of Vegetable Particles, which it received from Vegetable Exhalations in the Atmosphere; tho’ not so great a Quantity as Rain-water, that comes immediately thence.
These, I have to do with, are the Particles which Plants have from the Earth, or Soil; but they have also fine Particles of Earth from Water, which may impart some of its finest Charge to the Superficies of Roots, as well as to the Superficies of the Parts of the Earth[15] which makes the Pasture of Plants.
[15]If Water does separate, and take any of the mere Pabulum of Plants from the Soil, it gives much more to it.
Yet it seems, that much of the Earth, contain’d in the clearest Water, is there in too large Parts to enter a Root; since we see, that in a short time the Root’s Superficies will, in the purest Water, be cover’d with Earth, which is then form’d into a terrene Pasture, which may nourish Roots; but very few Plants will live long in so thin a Pasture, as any Water affords them. I cannot find one as yet that has liv’d a Year, without some Earth have been added to it.
And all Aquatics, that I know, have their Roots in the Earth, tho’ cover’d with Water.
The Pores, Cavities, or Interstices of the Earth, being of two Sorts, viz. Natural and Artificial; the one affords the Natural, the other the Artificial Pasture of Plants.
The natural Pasture alone will suffice, to furnish a Country with Vegetables, for the Maintenance of a few Inhabitants; but if Agriculture were taken out of the World, ’tis much to be fear’d, that those of all populous Countries, especially towards the Confines of the frigid Zones (for there the Trees often fail of producing Fruit), would be oblig’d to turn Anthropophagi, as in many uncultivated Regions they do, very probably for that Reason.