TRUNK. 



of the cellular fubftauce, in which the feveral fluids of it are 

 elaborated and prepared. 



A true and fomewhat inner bark is fituated next to 

 the above in the trunk of the tree, and is of a hard 

 texture, but adhering only loofely in trees to the cover- 

 ing which lies below it. In tender plants this covering 

 is often of a foft pulpy nature, and has the denomination of 

 ilcin. 



A ftill more inner layer, which is often called liler, forms 

 a third part or covering of the trunk in trees, which is of a 

 membranous and flexile nature, being fometimes altogether 

 feparable from the true bark above it, and the white lamina 

 which lies below it. This and the former coat of the trunks 

 in trees are formed of different lamina, as is evident from 

 macerating them in water, by whicli the cellular fubftance is 

 deftroyed, and the laminated appearance becomes fully dif- 

 played. Thefe feem to be parts which are very eflential to 

 tlie life of the plant or vegetable, as in them the chief or 

 principal funftions of it are carried on ; fuch, for inftance, as 

 thofe of nutrition, digeftion, fecretion, and fome others. 

 This is plainly proved and (hewn to be the cafe, by thofe 

 trees which have hollow or rotten trunks, the infides being 

 wholly deftroyed, and by fuch plants as are kept in vigour 

 by the perfeftly good ftate of their barks, although the 

 internal parts of their trunks or ftalks are wholly rotten and 

 deftroyed. 



The next part, lamina, or coat, which affords a covering or 

 portion to the truuks in trees, is that which has the title of 

 alburnum or fapwood commonly given to it, and which is 

 fituated immediately upon the ligneous or woody part, being 

 moftly compofed of a rather foft white fubftance that is 

 fcarcely perceptible in fome forts of trees, but which in others 

 is hard and perfectly vifible, as in thofe of the oak, elm, 

 and fome other kinds. This coat or part forms an imperfeft 

 fort of wood in the trunk, not having yet put on the con- 

 fiftence which is proper for perfeft wood, the former of 

 which muft be arrived at before the latter can be put on. 

 The hardnefs and folidity of this part of the trunk are 

 fomewhat in proportion to the vigour of growth in the 

 particular tree or plant. 



The fucceeding or ligneous part, is that which is com- 

 pofed of a compaft fibrous fubftance, difpofed in concentric 

 la^'ers, and which furrounds the middle or pithy part of the 

 trunks. It feems as if it were conftituted or made up of a 

 congeries or colleftion of dried vafcular parts ; and in plants 

 of the annual and biennial kinds commonly receives the de- 

 nomination of fledi. 



The laft, middle, or pithy part of the trunks of trees or 

 plants, is that which is fituated in and runs through the 

 hearts of them, and which is of a foft vafcular nature, dif- 

 fering from that of the cellular textured kind in the perfeft 

 whitenefs of its colour. It is in the greateft abundance 

 while the trees or plants are in their young ftate of growth, 

 diminifhing in quantity as they advance in age and fize, and 

 at length not unfrequently wholly difappearing. Hence it 

 is obvioufly neceflary to them in the beginning of their lives 

 and growths, but not for the continuance of them. It has 

 been fuggefted as probable, that nature may referve a fuper- 

 fluous nouriftiing fluid in this pithy part, if from any caufe 

 the young tree or plant ftiould become dry, that then it may 

 be taken up and converted into its food and fupport. 



It muft be evident, that what has been faid concerning the 

 trunks of trees and plants, muft be equally apphcable in 

 every refpeft to the branches and other ramifications, as 

 having the fame parts continued from fuch trunks, of which 

 they in faft form a part in the ways which have already been 

 pointed out. 



The trunks of trees and other vegetable produttions 

 during their growths are enlarged in their fize and thicknefs 

 throughout their whole lengths, as well as in their heights, 

 and not at any one particular point or part only, as has been 

 fully proved by numerous and repeated trials of various 

 kinds. And in thofe which are only of an annual or one 

 year's growth and duration, the enlargement or expanfion in 

 length continues fimply until they have protruded and com- 

 pleted their flowers and flowering procefs, when the con- 

 ftituent parts of the trunks, ftems or ftalks begin to take 

 on a hardened form, and at length, in a gradual manner, be- 

 come quite dry and rigid. 



But in thofe which are of a perennial nature, or of fome 

 years' growth and duration, this enlargement or increafe in 

 the trunks, ftems, or ftalks, continues until fuch times as 

 the leaves decay and fall off in the autumnal feafon, when a 

 germ or bud protrudes and fixes itfelf in the place which 

 contains the bafis or rudiment of a new trunk or ftem, that 

 by degrees during the winter months increafes in fize until the 

 advance of the vernal feafon, when, throwing off its former 

 covering, it continues the enlargement or increafe of the new 

 trunk or ftem, in the fame manner as the inferior or lower 

 part was augmented during the former year ; as in the place 

 where a bud is fituated, a fwelhng-out takes place and ex- 

 tends itfelf, which is fo continued with the new trunk or 

 ftem, as fcarcely to leave any mark or veftige where it was. 

 The increafe of the trunks- or ftems in breadth, however, 

 docs not proceed from the dilatation or enlargement of the 

 woody layers of them, but from the generation and produc- 

 tion of new laminae or layers, which are every year dcpofited 

 and added to them, by the veffels which are contained in the 

 barks of them, as has been fufiiciently fhewn by different 

 experiments. 



It has been further fliewn by obfervation and experience, 

 that the trunks or ftems of trees and fome other plants are 

 augmented every year by two woody lamina; or layers, but 

 that the fize or thicknefs of them is by no means each year 

 exaftly the fame, this depending in fome meafure upon the 

 vigour of growth, age, and ftate of the chmate, as they are 

 the greateil when the ftate of growth is the moft, the age in 

 the middle degree, and the heat of the fituation moderate ; 

 for the warmer the fummer, the more flender the bark, or 

 outward covering. 



The trunks, or ftems and ftalks, in trees and plants, are 

 of feveral different kinds, and diftinguifhed by many dif- 

 ferent names. Some trees have trunks or ftems which are 

 very ftiort and thick, others have long large clean ones ; and 

 fome again have them long, fmall, and clean, otliers more 

 knotty ; fome are very crooked, others quite ftraight ; and 

 there are ftill many further differences in thefe and feveral 

 other rcfpefts. Trees of the oak, afli, beech, and elm 

 kinds, and the feveral forts of the fir-tribe, have, in general, 

 the largeft, thickeft, and cleareft trunks or bolls ; but there 

 are many other varieties of trees which furnifli good ufeful 

 trunks and ftems, fuch as the lime, the walnut, the willow, 

 the poplar, the chefnut, &c. in particular fituations. The 

 trunks of trees are valuable as timber, according to the par- 

 ticular ufes and purpofes for which they are defigned, and to 

 which they are put. Thus in fliip-building, their being pro- 

 perly crooked is a great recommendation ; while in many 

 works of carpentry and other defcriptions, their being pcr- 

 feftly ftraight renders them of the moft eftimation. In faft, 

 their having a ftraight clean growth is in general a favourable 

 property, and a circumftance which makes them readily dif- 

 pofed of in the markets. 



In plants of otlicr kinds the trunks are often fmall, fo 

 as more properly to defcrve the title of ftems ; and at other 



times 



