is impregnate with divers effential Tinctures, as it is continually filter'd from the Fibres of one Kind to thofe of another. We may obferve in Figure the First, very plainly, the Infertions of the Cortical Body as they run from the Centre to the Circumference, which in other Subjects are visibly braced and interwoven together by Capillary Tubes with the Longitudinal Veffels of the Wood, and by that Means conftitute a firm Body, as the Timber of any Tree.

From hence we do not only learn, that in all Plants there is a Neceffity of two specifically diftinct Juices to act upon one another, but that these in their Action are filter'd or refin'd, alter'd and chang'd, according to the Parts they pass through, and also that in fome Parts they fooner ripen and become prolifick than in others; they are alfo more grateful to the Smell in fome Parts than in others: Nor is this all; this mixing, filtering and ripening, fooner or later, of the Juices, gives Difference of Colour to the feveral Parts of the Plant, and is feemingly the Occafion of most of the Alterations which we find in the feveral Parts of Trees.

Dr. Grew fuppofes the chief governing Principle in the Juices of Plants to be the Saline; which Saline Principle he tells us must be understood as a Generick Term, under which divers Species are comprehended. The Vegetable Salts feem to be four, viz. the Nitrous and Acid, Alkaline and a Marine; arguing, firft, from the Cuticular and other Concretion, commonly call'd Moldinefs or Mother, in Liquors diftill'd from Herbs, Vinegar,

and

and fuch-like; for in thefe, fays he, there is a Tendency to Vegetation, and many of them are true Vegetables, as Dr. Hook has ob ferv'd in his Micrographia, and has been confirm'd by others. Now the Liquors where thefe are found, do wholly, or in part, lofe their Taste and Smell, and become Vapid, the more fenfible Principles therein having made their Tranfit from the Fluid into the concrete Parts.

But in a more particular manner my Au thor obferves, the Nitrous Salts feem to be affign'd by Nature chiefly for the Growth of Plants; the other three Salts are exhibited by the feveral Ways of refolving the Principles of a Plant, fome in their natural State yield an Acid Juice, others by Fermentation, and moft by Diftillation in a fand Furnace, yield an acid Liquor.

By Calcination, all Plants yield more or lefs both of a fix'd and volatile alkalous Salt, the first in the Afhes, the latter in the Soot ; but the Marine Salt is obtain'd no other way but from a Solution of the Alkaline upon its being expos'd to the Air.

The Diversity of Salts found in one Plant ferves not only as a Proof of what has been related above, but has given the Hint to Physicians, of ufing fometimes one Part of a Plant, and fometimes another, as the Case of their Patient requir'd': The Root is serviceable on fome Accounts, the Bark in others, the Wood in others; the Flowers, Fruit, and the naked Seeds, have all their several distinct Virtues. But because it is not in every ones way to extract the Salts from Plants, as has

been

been related, I fhall here infert à Method pres fcrib'd to know what Salt is moft prevailing in every Plant, but chiefly in their flowering Parts, which perhaps may be worth the Trial of the Curious, but I have not yet had an Opportunity to try it; for could we once judge rightly of the Quantity of each refpective Salt refiding in a Plant, we might have a furer Guefs at the Manner proper to improve their Vegetation, which is the Point we are now upon.

Table

1

Table of Experiments recommended by

Dr. Grew.

Accharum Saturni drop'd on a Tincture of
Red Rofes makes a faint pale Green.

Salt of Tartar upon the fame, a deeper
Green.

Spirit of Hartfhorn on the Tincture of Burrage and Larkheel Flowers, makes a Verdigrease Green.

The fame Spirit upon green Leaves does not change them; which feems to intimate, that fome Alkaline Salt in the Air is predominant in the Production of Green in Plants.

Salt of Tartar on White Daisy Flowers, changes them to a light Green.

Spirit of Sulphur on green Leaves of Adonis Flower, Everlasting Peafe, Holy-oak, changes them yellow.

Spirit of Sulphur on the yellow Flower of Crow-foot, alters not. And the Doctor obferves, that in Yellows the Sulphureous Acid and Alkaline Parts are all more equal; but I rather think they confift chiefly of Sulphur, because Sulphur with Sulphur can produce no Change.

Spirit of Sulphur on Tincture of Clove-gillyflower makes a bright Blood Red; so that Y

as

as Alkalies or other analogous Salts are predominant in Greens, Acids are in Red.

Spirit of Sulphur on Tincture of Violets, turns it from Blue to a true Lake or middle Crimfon.

When Sulphur and the Alkaline Salts are more equal, they produce Tawny.

When Sulphur, Acid and Alkaline, Yellow.

When Sulphur is predominant, and the Acid and Alkaline equal, they produce Blue.

When Sulphur and Acid are predominant to the Alkaline, then Purple.

When Sulphur is predominant to the Alkaline, and the Acid to them both, then Scarlet. When Acid is predominant to the Alkaline, and Sulphur to both, then Blood Red.

To give my Reader fome further Hints relating to the Colours obfervable in Plants, I fhall infert the Copy of a Letter which I writ to my learned and ingenious Friend the late Mr. James Petiver, F. R. S. Anno 1717, which more efpecially I chufe to do in this Place because it relates to fome Experiments I have already made, and to fome others which I think may be neceffary to make, towards finding out the effential Parts of Plants, and may lead us more precifely into, the way of improving their Growth,

To