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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 ufe 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 mechanifm 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 alfo, 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 organised system 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 trachea 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, firft 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; 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 eafy to fay. It seems 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 ascending and descending 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

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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 absorbent veffels, whether of the root, trunk, or branches, are variously mixed, feparated, 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 elastic 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 fuppofed to perform all forts of chemical operations. Whence it fhould follow, that the air contains all forts of chemic productions, the vapours, fumes, oils, falts,

(4 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 digestions, till fuch time as they affume the most 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-exifting juices, fhould fo alter the fine nourishment drawn from earth and air (a), as to produce various fpecific qualities of great efficacy in medicine: especially if it be confidered that in the opinion of learned men, there is an influence on plants derived from the fun, befides it's mere heat. Certainly doctor Grew, that curious anatomift 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 so say, of animals or vegetables, consists of oily, aqueous, and faline particles, which being dif folved, volatilised, and diverfly agitated, part thereof is spent and exhaled into the air; and that part which remains is by the oeconomy 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 answer the panniculus adipofus in animals, defending trees from the weather, and, when in fufficient quantity, rendering them evergreen. This balfam, weeping or fweating through the bark, hardens into refin; and this most copiously in the feveral species of pines and

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firs, whofe oil being in greater quantity, and more tenacious of the acid fpirit or vegetable foul (as perhaps it may not improperly be called) abides the action of the fun, and attracting the fun beams, is thereby exalted and enriched, fo as to become a moft noble medicine; fuch is the laft product of a tree, perfectly maturated by time and fun.

39. It is remarked by Theophraftus, that all plants and trees while they put forth have most humour, but when they have ceafed to germinate and bear, then the humour is strongest and most fheweth the nature of the plant, and that, therefore, trees yielding refin fhould be cut after germination. It seems alfo very reasonable to fuppofe the juice of old trees, whofe organs bring no new fap, fhould be better ripened than that of others.

40. The aromatic flavours of vegetables feem to depend upon the fun's light, as much as colours. As in the production of the later, the reflecting powers of the object, fo in that of the former, the attractive and organical powers of the plant co-operate with the fun (a). And as from Sir Ifaac Newton's experiments it appears, that all colours are virtually in the white light of the fun, and fhew themselves when the rays are separated by the attracting and repelling powers of objects, even so the specific qualities of the elaborate juices of plants, feem to be virtually or eminently contained in the folar light, and are actually exhibited upon the feparation of the rays, by the peculiar powers of the capillary organs in vegetables, attracting and imbibing certain rays, which produce certain flavours and qualities, in like manner as certain rays, being reflected, produce certain coIcurs,

(a) 36, 37.

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