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light ; which at the same time that it heats, doth wonderfully rarefy and raise the fap; till it perspires and forms an atmosphere, like the effluvia of animal bodies. And though the leaves are suppos. ed to perform principally the office of Jungs, breathing out excrementitious vapours, and drawing in alimentary; yet it seems probable, that the reciprocal actions of repulsion and attraction are performed all over the surface of vegetables, as well as animals. In which reciprocation, Hippocrates supposeth the manner of nature's acting, for the nourishment and health of animal bodies, chiefly to consist. 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 fay. It seems very considerable and altogether necessary, as well to vegetable as animal life.
34. It is an opinion received by many, that the sap circulates in plants as the blood in animals: that it ascends through capillary arteries in the trunk, into which are inofculated other vessels of the bark answering to veins, which bring back to the root the remainder of the fap, over and above what had been deposited, during it's ascent by the arterial veffels, and fecreted for the several uses of the vegetable throughout all it's parts, ftem, branches, leaves, Powers, 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 defcending juices; while some will have the ascent and defcent to be a circulation of the fame juices through different vessels: others will have the ascending juice to be one fort attracted by the root, and the descending another imbibed hy the leaves, or extremities of the branches : Jastly, others think that
the same juice, as it is rarefied or condensed by heat or cold, rises and subsides in the fame tube. I shall not take upon me to decide this controversy. Only I cannot help observing, that the vulgar ar. gument from analogy between plants and animals Jofeth much of it's force, if it be confidered, that the suppoled circulating of the sap, from the root or lacteals through the arteries, and thence return, ing, by inofculations, through the veins or bark vefsels to the root or lacteals again, is in no fort conformable or analogous to the circulation of the blood.
35. It is sufficient to observe, what all muft acknowledge, that a plant or tree is a very nice and complicated machine (a); by the several parts and motions whereof, the crude juices admitted through the absorbent veffels, whether of the root, trunk, or branches, are variously mixed, separated, alter. ed, digerted, and exalted in a very wonderful manner. The juice as it passeth in and out, up and down, through tubes of different textures, shapes, and fizes, and is affected by the alternate compression and expansion of elastic vessels, by the viciffitudes of feasons, the changes of weather, and the various action of the solar light, grows ftill more and more elaborate.
36. There is therefore no chemistry like that of nature, which addech 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 sorts 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 sorts of chemic productions, the vapours, fumes, oils, falts,
and spirits of all the bodies we know :" from which general aggregate or mass, those that are proper being drawn in, through the fine veffels of the leaves, branches, and item of the tree, undergo in it's various organs, new alterations, secretions, and digestions, till such time as they assume 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-existing juices, 11.ould so alter the fine nourishment drawn from earth and air (a), as to produce various specific qualities of great efficacy in medicine : especially if it be considered that in the opinion of learned men, there is an influence on plants derived from the sun, beides it's niere heat. Certainly doctor Grew, the curious anatomist of plants, holds the folur influence to differ from that of a mere culinary fire, otherwise than by being only a more temperate and equal hear.
38. The alimentary juice taken into the lacteals, if I
may so say; of animals or vegetables, conlists of oily, aqueous, and faline particles, which being difsolved, volatilised, and diversiy agitated, pare 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 inspiílated oil or balsam, and deposited in certain cells placed chiefly in the bark, which is thought to answer the panniculus adiposus in animals, defending trees from the weather, and, when in fufficient quantity, rendering them evergreen. This balsam, weeping or sweating through the bark, hardens into refin
; and this moft copiously in the several species of pines and
firs, whose oil being in greater quantity, and more tenacious of the acid spirit or vegetable soul (as perhaps it may not improperly be called) abides the action of the sun, and attracting the fun beams, is thereby exalted and enriched, lo as to become a most noble medicine ; such is the last product of a tree, perfectly maturated by time and fun.
39. It is remarked by Theophrastus, that all plants and trees while they put forch have most humour, but when they have ceased to germinate and bear, then the humour is strongest and most sheweth the nature of the plant, and that, therefore, trees yielding refin should be cut after-germination. It seems also very reasonable to suppose the juice of old trees, whose organs bring no new sap, should be better ripened than that of others.
40. The aromatic Aavours of vegetables seem to depend upon the sun's light, as much as colours. As in the production of the later, the reflecting powers of the object, so in that of the former, the attractive and organical powers of the plane co-operate with the lun (a). And as from Sir Ifaac Newton's experiments it appears, that all colours are virtually in the white light of the sun, and shew 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, seem to be virtually or eminently contained in the solar light, and are actually exhibited upon the separation of the rays, by the peculiar powers of the capillary organs in vegetables, attracting and imbibing certain rays, which produce certain favours and qualities, in like manner as certain rays, being reflected, produce certain colours,
(a) 36, 379
41. It hath been observed by some curious anatomists, that the secretory vessels in the glands of animal bodies are lined with a fine down, which in different glands is of different colours. And it is thought, that each particular down, being originally imbued with it's own proper juice, attracts none but that fort ; by which means to many various juices are secreted in different parts of the body. And perhaps there may be something analogous to this, in the fine absorbent vessels of plants, which may co-operate towards producing that endless variety of juices, elaborated in plants from the same earch and air.
42. The balsam or effential oil of vegetable contains a spirit, wherein consist the specific qualities, the smell and taste of the plant. Boerhaave holds the native presiding spirit to be neither oil, falt, earth, or water ; but somewhat too fine and subtile to be caught alone and rendered visible to the eye. This when suffered to fly off, for instance, from the oil of rosemary, leaves it deftitute of all favour. This fpark of life, this fpirit or soul, if we may so say, of the vegetable departs without any sensible diminution of the oil or water wherein it was lodged.
43: It should seem that the forms, souls, or principles of vegetable life, sublift in the light or solar emanation (a), which in respect of the macrocosm is what the animal fpirit is to the microcosm ; the interior tegument, the subtile inftrument and vehicle of power. No wonder then that the ens primum or scintilla spirituosa, as it is called, of plants should be a thing so fine and fugacious as to escape our nicest search. It is evident that nature at the sun's approach vegetales; and