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the fun or the north wind, are reckoned by Theophraftus to produce the beft and pureft tar: And the Idæan pines were diftinguished from those growing on the plain, as yielding a thinner, sweeter, and better fcented tar, all which differences I think I have obferved, between the tar that comes from Norway, and that which comes from low and (wampy countries.

29. Agreeably to the old obfervation of the Peripatetics, that heat gathereth homogeneous things and difperfeth fuch as are heterogeneous, we find chemistry is fitted for the analysis of bodies. But the chemistry of nature is much more perfect than that of human art, inafmuch as it joineth to the power of heat that of the most exquifite mechanism. Those who have examined the structure of trees and plants by microscopes, have difcovered an admirable variety of fine capillary tubes and veffels, fitted for feveral purposes, as the imbibing or attracting of proper nourishment, the diftributing thereof through all parts of the vegetable, the discharge of fuperfluities, the fecretion of particular juices. They are found to have ducts answering to the tracheæ in animals, for the conveying of air; they' have others answering to lacteals, arteries, and veins. They feed, digeft, refpire, perfpire and generate their kind, and are provided with organs nicely fitted for all thofe ufes.

30. The fap veffels are obferved to be fine rubes running up through the trunk from the root. Secretory veffels are found in the bark, buds, leaves, and flowers. Exhaling veffels for carrying off excrementitious parts, are difcovered throughout the whole furface of the vegetable. And (though this point be not fo well agreed) doctor Grew in his Anatomy of plants, thinks there appears

4

a cir.

circulation of the fap, moving downwards in the root, and feeding the trunk upwards.

31. Some difference indeed there is between learned men, concerning the proper use of certain parts of vegetables. But whether the difcoverers have rightly gueffed at all their ufes or no, thus much is certain, that there are innumerable fine and curious parts in a vegetable body, and a wonderful fimilitude or analogy between the mechanism of plants and animals. And perhaps fome will think it not unreasonable to fuppofe the mechaniím of plants more curious than even that of animals, if we confider not only the feveral juices fecreted by different parts of the fame plant, but also, the endless variety of juices drawn and formed out of the fame foil, by various fpecies of vegetables; which must therefore differ in an endless variety, as to the texture of their abforbent veffels and fecretory ducts.

32. A body, therefore, either animal or vegetable, may be confidered as an organifed fyftem of tubes and veffels, containing feveral forts of fluids. And as fluids are moved through the veffels of animal bodies, by the fyftole and diastole of the heart, the alternate expanfion and condensation of the air, and the ofcillations in the membranes and tunicks of the veffels; even fo by means of air expanded and contracted in the tracheæ or veffels made up of elaftic fibres, the fap is propelled through the arterial tubes of a plant, and the vegetable juices, as they are rarefied by heat or condenfed by cold, will either afcend and evaporate into air, or defcend in the form of a grofs liquor.

33. Juices therefore, first purified by ftraining through the fine pores of the root, are afterwards exalted by the action of the air and the veffels of the plant, but, above all, by the action of the fun's

light;

light; which at the fame time that it heats, doth wonderfully rarefy and raise the fap; till it perfpires and forms an atmosphere, like the effluvia of animal bodies. And though the leaves are fuppofed to perform principally the office of lungs, breathing out excrementitious vapours, and drawing in alimentary; yet it feems probable, that the reciprocal actions of repulfion and attraction are performed all over the furface of vegetables, as well as animals. In which reciprocation, Hippocrates fuppofeth the manner of nature's acting, for the nourishment and health of animal bodies, chiefly to confift. And, indeed, what share of a plant's nourishment is drawn through the leaves and bark, from that ambient heterogeneous fluid called air, is not easy to say. It feems very confiderable and altogether neceffary, as well to vegetable as animal life.

34. It is an opinion received by many, that the fap circulates in plants as the blood in animals: that it afcends through capillary arteries in the trunk, into which are inofculated other veffels of the bark answering to veins, which bring back to the root the remainder of the fap, over and above what had been depofited, during it's afcent by the arterial veffels, and fecreted for the feveral ufes of the vegetable throughout all it's parts, ftem, branches, leaves, flowers, and fruit. Others deny this circulation, and affirm that the fap doth not return through the bark veffels. It is nevertheless agreed by all, that there are afcending and defcending juices; while fome will have the afcent and defcent to be a circulation of the fame juices through different veffels: others will have the afcending juice to be one fort attracted by the root, and the defcending another imbibed by the leaves, or extremities of the branches: laftly, others think that C

the

the fame juice, as it is rarefied or condensed by heat or cold, rifes and fubfides in the fame tube. I fhall not take upon me to decide this controversy. Only I cannot help obferving, that the vulgar argument from analogy between plants and animals Jofeth much of it's force, if it be confidered, that the fuppofed circulating of the fap, from the root or lacteals through the arteries, and thence returning, by inofculations, through the veins or bark veffels to the root or lacteals again, is in no fort conformable or analogous to the circulation of the blood.

35. It is fufficient to obferve, what all must acknowledge, that a plant or tree is a very nice and complicated machine (a); by the feveral parts and motions whereof, the crude juices admitted through the abforbent veffels, whether of the root, trunk, or branches, are variously mixed, separated, altered, digested, and exalted in a very wonderful manner. The juice as it paffeth in and out, up and down, through tubes of different textures, fhapes, and fizes, and is affected by the alternate compreffion and expansion of elaftic veffels, by the viciffitudes of feafons, the changes of weather, and the various action of the folar light, grows ftill more and more elaborate.

36. There is therefore no chemistry like that of nature, which addeth to the force of fire, the most delicate, various, and artificial percolation (b). The inceffant action of the fun upon the elements of air, earth, and water, and on all forts of mixed -bodies, animal, vegetable and foffil, is supposed to perform all forts of chemical operations. Whence it should follow, that the air contains all forts of chemic productions, the vapours, fumes, oils, falts,

(a 30, 31.

(b) 29.

and

and fpirits of all the bodies we know from which general aggregate or mafs, thofe that are proper being drawn in, through the fine veffels of the leaves, branches, and ftem of the tree, undergo in it's various organs, new alterations, fecretions, and digeftions, till fuch time as they affume the moft elaborate form.

37. Nor is it to be wondered, that the peculiar texture of each plant or tree, co-operating with the folar fire and pre-existing juices, fhould fo alter the fine nourishment drawn from earth and air (a), as to produce various fpecific qualities of great effica cy in medicine: especially if it be confidered that in the opinion of learned men, there is an influ ence on plants derived from the fun, befides it's mere heat. Certainly doctor Grew, that curious anatomist of plants, holds the folar influence to differ from that of a mere culinary fire, otherwise than by being only a more temperate and equal

heat.

38. The alimentary juice taken into the lacteals, if I may fo fay, of animals or vegetables, confifts of oily, aqueous, and faline particles, which being dif folved, volatilifed, and diverfly agitated, part thereof is spent and exhaled into the air; and that part which remains is by the economy of the plant, and action of the fun, ftrained, purified, concocted, and ripened into an infpiffated oil or balfam, and depofited in certain cells placed chiefly in the bark, which is thought to anfwer the panniculus adipofus in animals, defending trees from the wea ther, and, when in fufficient quantity, rendering them evergreen. This balfam, weeping or fweating through the bark, hardens into refin; and this moft copiously in the feveral fpecies of pines and

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