No one Truth can possibly contradict or interfere with any other Truth; but one Error may contradict and interfere with another Error, viz.
Mr. Bradley, and all Authors, I think, are of Opinion, that Plants of different Natures are fed by a different Sort of Nourishment; from whence they aver, that a Crop of Wheat takes up all that is peculiar to that Grain; then a Crop of Barley all that is proper to it; next a Crop of Pease, and so on, ’till each has drawn off all those Particles which are proper to it; and then no more of these Grains will grow in that Land, till by Fallow, Dung, and Influences of the Heavens, the Earth will be again replenish’d with new Nourishment, to supply the same Sorts of Corn over again. This, if true (as they all affirm it to be), would prove, that the Air is not the Food of Vegetables. For the Air being in itself so homogeneous as it is, could never afford such different Matter as they imagine; neither is it probable, that the Air should afford the Wheat Nourishment more one Year, than the ensuing Year; or that the same Year it should nourish Barley in one Field, Wheat in another, Pease in a Third; but that if Barley were sown in the Third, Wheat in the First, Pease in the Second, all would fail: Therefore this Hypothesis of Air for Food interferes with, and contradicts this Doctrine of Necessity of changing Sorts.
I suppose, by Air, they do not mean dry Particles of Earth, and the Effluvia which float in the Air: The Quantity of these is too small to augment Vegetables to that Bulk they arrive at. By that way of speaking they might more truly affirm this of Water, because it must be like to carry a greater Quantity of Earth than Air doth, in proportion to the Difference of their different specific Weight; Water, being about 800 times heavier than Air, is likely to have 800 times more of that terrestrial Matter in it; and we see this is sufficient to maintain some Sort of Vegetables, as Aquatics; but the Air, by its Charge of Effluvia, &c. is never able to maintain or nourish any Plant; for as to the Sedums, Aloes, and all others, that are supposed to grow suspended in the Air, ’tis a mere Fallacy; they seem to grow, but do not; since they constantly grow lighter; and tho’ their Vessels may be somewhat distended by the Ferment of their own Juices which they received in the Earth, yet suspended in Air, they continually diminish in Weight (which is the true Argument of a Plant) until they grow to nothing. So that this Instance of Sedums, &c. which they pretend to bring for Proof of this their Hypothesis, is alone a full Confutation of it.
Yet if granted, that Air could nourish some Vegetables by the earthy Effluvia, &c. which it carry’d with it[6]; even that would be against them, not for them.
[6]This is meant of dry Earth, by its Lightness (when pulveriz’d extremely fine) carried in the Air without Vapour: For the Atmosphere, consisting of all the Elements, has Earth in it in considerable Quantity, mix’d with Water; but a very little Earth is so minutely divided, as to fly therein pure from Water, which is its Vehicle there for the most Part.
They might as well believe, that Martins and Swallows are nourish’d by the Air, because they live on Flies and Gnats, which they catch therein; this being the same Food, which is found in the Stomach of the Chameleon.
If, as they say, the Earth is of little other Use to Plants, but to keep them fix’d and steady, there would be little or no Difference in the Value of rich and poor Land, dung’d or undung’d; for one would serve to keep Plants fix’d and steady, very near, if not quite as well as the other.
If Water or Air was the Food of Plants, I cannot see what Necessity there should be of Dung or Tillage.
4. Fire. No Plant can live without Heat, tho’ different Degrees of it be necessary to different Sorts of Plants. Some are almost able to keep Company with the Salamander, and do live in the hottest Exposures of the hot Countries. Others have their Abode with Fishes under Water, in cold Climates: for the Sun has his Influence, tho’ weaker, upon the Earth cover’d with Water, at a considerable Depth; which appears by the Effect the Vicissitudes of Winter and Summer have upon subterraqueous Vegetables.
Tho’ every Heat is said to be a different Degree of Fire; yet we may distinguish the Degrees by their different Effects. Heat warms; but Fire burns: The first helps to cherish, the latter destroys Plants.