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the sun or the north wind, are reckoned by Theophrastus to produce the best and purest tar: And the Idæan pines were distinguished from those growing on the plain, as yielding a thinner, sweeter, and better scented tar, all which differences I think I have observed, between the tar that comes from"Norway, and that which comes from low and swampy countries.
29. Agreeably to the old observation of the Peripatetics, that heat gathereth homogeneous things' and disperscth such as are heterogeneous, we find' chemistry is fitted for the analysis of bodies. But the chemistry of nature is much more persect than that of human art, inasmuch as it joineth to the/ , power of heat that of the most exquisite mechanism. Those who have examined the structure of trees and plants by microscopes, have discovered an admirable variety of fine capillary tubes and vessels, fitted for several purposes, as the imbibing or attracting' of proper nourishment, the distributing thereof through all parts of the vegetable, the discharge of superfluities, the secretion of particular juices; They are found to have ducts answering to the tracheae in animals, for the conveying of air*, they have others answering to lacteals, arteries, and veins. They seed, digest, respire, perspire and generate their kind, and are provided with organs nicely fitted for all those uses.
30. The fap vessels are observed to be sine tubes running up through the trunk from the root. Secretory vessels are found in the bark, buds, leaves, and flowers. Exhaling vessels for carrying off excrementitious. parts, are discovered throughout the whole surface of the vegetable. And (though this point be not so well agreed) doctor Grew in his Anatomy of plants, thinks there appears
acirea circulation of the fap, moving downwards in the root, and seeding the trunk upwards.
31. Some disserence indeed. there is between learned men, concerning the proper use of certain parts of vegetables. But whether the discoverers have rightly guessed ac all their uses or no, thus much is certain, that. there are innumerable fine and curious parts in a vegetable body, and a wondersul similitude or analogy between the mechanism of plants and animals. And perhaps some will think it not unreasonable to suppose the mechanism of plants more curious than even that of animals, if we consider not only the several juices secreted by different parts of the fame plant, but also, the endless variety of juices drawn and formed out of the fame foil, by various species of vegetables; which must therefore differ in an endless variety, as to the texture of their absorbent vessels and secretory ducts.
32. A body, therefore, either animal or vegetable, may be considered as an organised system of tubes and vessels, containing several sorts of fluids. And as fluids are moved through the vessels of animal bodies, by the systole and diastole of the heart, the alternate expansion and condenfation of the air, and the oscillations in the membranes and tunicks of the vessels-, even so by means of air expanded and contracted in the tracheæ or vessels made up of elastic fibres, the fap is propelled through the arterial tubes of a plant, and the vegetable juices, as they are rarefied by heat or condensed by cold, will either ascend and evaporate into air, or descend in the form of a gross liquor.
33. Juices therefore, first purified by straining through the fine pores of the root, are afterwards exalted by the action of the air and vessels of the plant, but, above all, by the action of the sun's
light i light; which at the fame time that it heats, doth. -wondersully rarefy and raise the fap; till it perspires and forms an atmosphere, like the effluvia of animal bodies. And though the leaves are supposed to perform principally the office of lungs, 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, a$ -well as animals. In which reciprocation, Hippo-. crates supposeth the manner of nature's acting, far 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 al.-. together necessary, as well to vegetable as animal. lise.
34. It is an opinion received by many, that the. fap circulates in plants as the blood in animals i. that it ascends through capillary arteries in the trunk, into which are inosculated 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 vessels, and secreted for the several uses of the vegetable throughout all it's parts, stem, branches, leaves, flowers, and fruit. Others deny this circulation, and affirm that the fap doth not return through the bark vessels. It is nevertheless agreed by all, that there are ascending and descending juices; while some will have the ascent and descent to be a circulation of the fame juices throughdisferent vessels: others will have the ascending juice to be one sort attracted by the root, and the descending another imbibed by the leaves, or extremities of the branches: lastly, others think that
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the Tame 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 argument from analogy between plants and animals loseth much of it's force, if it be considered, that the supposed circulating of the fap, from the root or lacteals through the arteries, and thence returning, by inosculations, through the veins or bark vessels to the root or lacteals again, is in no sort conformable or analogous to the circulation of the blood.
35. It is sufficient to observe, what all must acknowledge, that a plant or tree is a very nice and complicated machine (a) 5 by the several parrs and motions whereof, the crude juices admitted through she absorbent vessels, whether of the root, trunk, or branches, are variously mixed, separated, altered, digested, 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 sizes, and is affected by the alternate Compression and expansion os elastic vessels, by the vicissitudes of seasons, the changes of weather, and the various action of the solar light, grows still 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 incessant action of the sun upon the elements of air, earth, and water, and on all sorts of mixed bodies, animal, vegetable and fossil, is supposed to perform all sorts of chemical operations. Whence it should follow, that the air contains all sorts of chemic productions, the vapours, sumes, 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 vessels of the , leaves, branches, and stem of the tree, undergo in its 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 solar fire and pre-existing juices, should so alter the fine nourishment drawn from earth and air (a), as to produce various specific qualities of great efficacy in medicine: especially is it be considered that io the opinion of learned men, there is an influence on plants derived from the sun, besides its Hlfre heat. Certainly doctor Grew, that curious anatomist of plants, holds the solar influence to difser 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 1 may so fay, of animals or vegetables, consists of oily, aqueous, and saline particles, which being dissolved, volatilised, and diverslyagitated, part thereof is spent and exhaled into the air; and that part which remains is by the ceconomy ot the plant, and action of the sun, strained, purified, concocted, and ripened into an inspissated oil or balfam, and deposited in certain cells placed chiefly in the bark, which is thought to answer the panniculus ddiposus in animals, desending trees from the weather, and, when in sufficient quantity, rendering them evergreen. This balfam, weeping or sweating through the bark, hardens into resin; and this most copiously in the several species of pines and