VEGETABLES. 



The fecond of thefe parft are tliofe which ftand next in 

 iiTiportance in vegetables, when confidered merely as fuch, 

 and which include the branches as well as all the more 

 folid parts of them, confiding pnncipally of different coats, 

 as bark, flefh or wood, according to the nature of the 

 vegetable, and pith, or the middle part. Thefe coats or 

 coverings are differently formed, modified, and conftituted, 

 fo as to be of different nfes in their economy. The part, 

 or layer, which is placed next to the wood, is compofed, in 

 vegetables of the tree kind, of a foft white fubftance, not 

 ealily difcernible in fome forts of trees, but harder and 

 more apparent in others. It is, as it were, an imperfeft 

 wood, or in the ftate between bark and wood. The wood is 

 the compaft, fibrous, hard part or fubftance which is dif- 

 pofed in the middle of trees, which in annual and biennial 

 vegetables is called the flelh, as has been feen already. 

 Between the above coat and the wood, a new ring of a 

 fofter nature is formed every year, which gradually lofes its 

 foftnefs as the cold feafon advances, and which towards the 

 middle of winter is converted into a folid ring of wood. 

 Thefe annual rings, which are vifible in moft trees when cut 

 through tranfverfely, ferve as marks by which to determine 

 their ages in fome cafes. They feem to decreafe in breadth 

 ES the trees advance in age ; and as they are found to be 

 very unequal throughout in their dimenfions, their breadth 

 probably varies as the feafon may be favourable or other- 

 wife. The wood, however, does not only differ from the 

 coats or bark in the degree of hardnefs, but likewife in its 

 ftruftiu'e, which is effentially different ; and the feeming 

 converfion of bark into wood, is imagined by fome to be 

 entii-ely a deception. 



Thus, if the branch, flem, or the root of a tree be cut 

 in a tranfverfe manner, it ufually difplays three diftincft 

 bodies or parts : the bark, the wood, and the pith ; each of 

 which is again fufceptible of a new divifion. The bark, 

 where perfeftly formed, has a thin covering, that may eafily 

 be feparatcd ; is in laminae or fcales, which, in old trees, are 

 moftly in a loofe and decaying ftate. It is not vafcular, 

 but merely defends the interior parts from injuries. It is 

 fuppofed to be a part of bttle importance in foreft-trees, 

 and the larger flirubs, the bodies of which are firm and of 

 ftrong texture ; but in the reeds, the graffes, and the plants 

 which have hollow ftalks, it is of great ufe, is of very great 

 ftrength, and appears conftituted of a fort of glaffy net- 

 work, which is chiefly liliceous earth, as has been lately 

 afcertained. This is the cafe in wheat, in the oat, and in 

 different other plants ; in fome of which it exifts in large 

 quantities, and is general in this part of tliofe of the hollow 

 kind. It is ferviceable as a fupport as well as proteftion 

 from infefts in fuch cafes. 



The moft interior part of the bark is compofed of layers, 

 the numbers of which vary with the age of the tree ; fo 

 that on cutting this part of a ti-ee of feveral years ftanding, 

 the produftions of different periods may be diftinftly feen, 

 though the layer of every particular year can rarely be 

 exaftly defined or afcertained. The funftions of the 

 different parts of the bark are of great importance to 

 vegetables. 



In regard to the wood in trees, it is compofed of an 

 external or linng part, called fap-wood, and of an internal 

 X)r dead part, termed heart-wood ; the former of which is 

 white, and full of moifture, and in young trees and annual 

 fhoots reaches even to the pith. It is the great vafcular 

 fyftem of the vegetable through which the fap-juice rifes, 

 the veffels in it extending from the leaves to the moil minute 

 filaments in the roots. Its ftruclure has different important 

 ufes in producing new arrarvgements, and forming new 

 wood. 



In refpeft to the arrangement of the fibres of the wood, there 



are two diftincl appearances in them : as the feries of white 

 fltining lamina, which fhoot from the centre towards the 

 circumference, and which conftitute what is termed the 

 Jilver grain of the wood ; and the numerous feries of con- 

 centric layers, which are commonly denominated the fpurious 

 grain, the number of which denotes the age of the tree, as 

 already fuggeiled. The former has many important func- 

 tions, and is the moil diftincl in foreft-trees ; though annual 

 fhrubs have even a fyftem of fibres fimilar to it. See Tim- 

 ber, Sap, and Alburnum. 



The ftem parts of fome vegetables are quite hollow ; 

 partly, it is fuppofed, from fuch vegetables requiring a 

 more than ordinary fupply of air in their fupport, as they 

 are generally thofe which are of a quick growth. 



The pith is the foft, white, innermotl fubllance of vege- 

 tables of the tree and other kinds, that is fituated in the 

 centres of the ftems. 



In the very infancy of the vegetable it occupies but a 

 fmall fpace, but gradually dilates ; and in ftioots of the 

 annual kind, and in yoimg trees, offers a confiderable dia- 

 meter. Being aftcd on by the heart-wood, as preffed by 

 the new layers of the fap-wood, in the more advanced age 

 of the tree, it begins to diminifh, and in very old foreft-trees 

 wholly difappears. As it has lately been whoUy removed 

 in different yoimg trees, which continued to live and in- 

 creafe ; it is evidently only an organ of fecondary im- 

 portance. In early ftioots, in vigorous growth, it is filled 

 \nth moifture, and is a refervoir of fluid nouriftiment, per- 

 haps, at the time when it is moft wanted. As the heart- 

 wood forms, it is more and more feparated from the living 

 part, the fap-wood ; its funClions become extindl, it dimi- 

 nifties, dies, and ultimately difappears. See Stalk and 

 Trunk. 



The third, or the leaves, are parts which are effential to 

 the exiftence of vegetables ; as when, either of the plant 

 or tree kind, wholly divefted, or only ftript of a con- 

 fiderable part of them, thev do not fhoot in a vigorous man- 

 ner. They are produced from the coats of the ftalks or 

 ftems, and are of the foft flelhy thick kind, or the more 

 thin, barky, or woody fort. They are capable of affording 

 nouriftiment, and of being of uie to vegetables, by the 

 nutrient fluid matters which they hold in referve in their 

 foft fubftances, and by the dew, air, and moifture, which, 

 they take in and th.rovv off. 



In all cafes the leaves are fimilar in their interior organi- 

 zation, and perform the fame funClions as the above parts, 

 only their ftrufttire is finer and more minute. The fap- 

 wood fpreads and extends itfelf from the footftalks into 

 the very extremities of the leaves ; it prefervcs a vafcular 

 fyilem, and its living powers ; fome parts of the former of 

 which may be diftindlly feen in the leaf. A material ufe 

 of the leaves is, the expofure of the fap to the influence of 

 the air, heat, and light : for which their furface is exten- 

 five, the tubes and cells very delicate, and their texture 

 porous and tranfparent. In the leaves, much of the water 

 of the fap is evaporated ; it is combmed with new princi- 

 ples, and fitted for its organizing fundlions, and probably 

 paffes, in its prepared ftate, from the extreme tubes of the 

 iap-v-'ood into the ramifications of the cortical tubes, and 

 then defcends through the bark. On the upper iurface of 

 leaves, which is expofed to the fun, the external covering 

 is thick but tranfparent, and is faid to be compofed of 

 matter poffeffed of little organization, which is either prin- 

 cipally earthy, or confifts of fome fubftance of the homo- 

 geneous chemical kind. That in the graffcs it is partly 

 filiceous, in the laurel refiiious, and in the thorn and maple 

 principally conftituted by a fubftance analogous to wax. 



By 



