« EelmineJätka »
the fun or the north wind, are reckoned by Theo. phrastus to produce the belt 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 obferved, between the tar that comes from Norway, and that which comes from low and swampy countries.
29. Agreeably to the old obfervation of the Peo. ripatetics, that heat gathereth homogeneous things and disperseth such 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, 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 fuperfluities, the secretion 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, digest, respire, perfpire and generate their kind, and are provided with organs nicely fitted for all those uses. - ..
30. The fap vessels are obferved to be fine cubes 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 difeovered 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
.. . a cir.
ea 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 discoverers have rightly guessed at all their uses 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 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 same plant, but also, the endless variety of juices drawn and formed out of the same foil, by various species of vegetables ; which must therefore differ in an endless variety, as to the texture of their absorbent vessels and recretory 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 Auids are moved through the vessels of animal bodies, by the systole and diastole of the heart, the alternate expansion and condensation 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; which at the fame 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 suppored to perform principally the office of lungs, breathing out excrementitious vapours and drawing in alimentary ; yer it seems probable, that the reciprocal actions of repullion and attraction, are performed all over the surface of vegetables, as well as animals. In which reciprocation, Hippo-. crates supposech che manner of nature's acting, for the nourishment and health of animal bodies, chie-, fly to consist. And, indeed, what share of a plant's nourishment is drawn through the leaves and bark, from chạt ambient heterogeneous fluid called air, is not easy to say. It seems very considerable and altogether necessary, as well co 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 inosculated ocher 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, Aowers, and fruit. Others deny: this circulation, and affirm that the fap doth noc. reçurn 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 same juices through different 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
the the same juice, as it is rarefied or condensed by heat or cold, rises and subsides in the same 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 Joseth much of it's force, if it be considered, that the supposed circulating of the sap, from the root or lacteals through the arteries, -and thence returning, by inofculations, through the veins or bark vessels 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 must 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 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 paffech in and out, up and down, through tubes of different textures, shapes, and sizes, and is affected by the alternate compression and expansion of elastic vefsels, by the vicissitudes of seasons, 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 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, fumes, oils, falts,
(a) 30, 31.
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, Tould so alter the fine nourilhment 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, besides its inere heat. Certainly doctor Grew, that curious. anatomist of plants, holds the solar influence to differ from that of a mere culinary fire, otherwise than by being only a more temperate and equal. heat.
33. The alimentary juice taken into the lacteals, if I may so fay, of animals or vegetables, consists of oily, aqueous, and saline particles, which being dissolved, volatilised, and diversly agitated, part thereof iş spent and exhaled into the air ; and that part which remains is by the economy of the plant, and action of the fun, strained, purified, concocted, and ripened into an inspiflated 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 sufficient quantity, rendering them evergreen. This balsam, weeping or sweating through the bark, hardens into resin ; and this most copiously in the several species of pines and