I shall consider Vegetable Substances with regard to Diet, in the first Place, because they are the Original Food of all Animals, who either immediately are nourished thereby, or else feed upon such Animals as are nourished by them.
Vegetables receive their Food from the Air and Earth, by means of several Recipient Vessels placed in the Root and Bark, (analogous to the Lacteals in Animals) conveyed and diluted by a sufficient Quantity of Water: This Food thus received, which I shall beg Leave to call Vegetable Chyle, is digested and assimilated in the Course of Circulation, through the Vessels of the Plant, till it is converted into Vegetable Substance, and is formed into the several differing Vegetable Juices, Gums, and Resins, that are peculiar to each Species of Plants. The Remainder, after the proper Separations, is evaporated thro’ the Pores of the Skin and through the Leaves, in the Manner of Animal Transpiration. I content myself here with this short Hint of Vegetable Nutrition, because I have treated it more at large and expresly in another Place: It is more material at present to examine the several Juices which circulate in the Vessels of Vegetables, because, in regard to Diet, they will appear to be the Matter of Animal Nutrition; for the Vessels of Plants are no other than meer Earth bound or connected together with Oyl, by the Means of some very powerful Attraction: This Earth is undissoluble by the utmost Force of Fire, since after burning a Plant in the open Fire, we find it left entire.
The Chyle of Plants seems to be made up of whatever Parts in the Earth are soluble in Water, so as to be capable of being received into the Absorbent or Recipient Vessels of Plants, before taken Notice of; and consequently may consist of Salts, Oyls, Fumes of Minerals, Metals, and other fossil Bodies, the putrified Parts of Animals and Vegetables. In its first State it is, to be sure, very crude; but by the Structure and Fabrick of the Plant, and the various Vessels it is strained thro’, it is changed, elaborated, secreted, and assimilated into the Substance of the Plant; whence it follows, that in Vegetables are contained Salts, Oyl, Water, and Earth, and probably Metals too, for the Ashes of Vegetables yield somewhat which the Load-Stone attracts.