| XXX | (43) | XXX |
AGRICULTURE. 4? deftined for the fecretion of turpentine ; and are fe from the feed: But in feme it is more immediately deii- fels, large, as to be diflindly vifible to the naked eye. ved from the bark. For the infertions of the bark runlies betwixt the bark and pith, and ning in betwixt the rays of the wood, meet in the centre, 2. Theof Wood two parts, viz. a parenchymatous, and ligand conilitute the pith. It is owing to this circumftance, confifls In all trees, the parenchymatous part of the wood, that among roots which have no pith in their lower nous. much diverfified as to fize and confidence, is uniparts, they are amply provided with it towards the top, though formly difpofed in diametrical rays, or infertions running as in columbine, lovage, 6v, fimilar rays of the lignous part. The bladders of the pith are of very different fizes, betwixt is nothing but a congeries of old dried and generally of a circular figure. Their pofition is_ The true wood Between the bark and the wood a new more uniform than in the bark. Their fides are not lymph-dudts. ring of thefe dudts is formed every year, which gradually mere films, but a compofition of fmall fibres or threads ; looies as the cold feafbn approaches, and, towhich gives the pith, when viewed with a microfcope, wards itsthefoftnefs middle of winter,' is condenfed into a felid the appearance of a piece of fine gauze, or net-work. ring of wood, Thefe annual rings, which are diftindtly We fhall conclude the defcription of roots, with ob- vifible trees when cut through, ferve as natural ferving, that their whole fubftance is nothing but a con- marks into moft diftinguifh their age. Plate V. fig. 1, 2. geries of tubes and fibres, adapted by nature for the abferption.of nourifhment, and of courfe the extenfion and The rings of one year are femetimes larger, fometimes fefs, than thofe- of another, probably owing to the favouraugmentation of their parts. ablenefs or unfavourablenefs of the feafon. Plate IV. Fig. 9. A tranfverfe fedtion of the root 3. The Pith, though of a different texture, is exof wormwood, as it appears actly of the fame fubftance with the parenchyma of the bark, and the infertions of the wood. The quantity of to the naked eye. Fig. 10. A fe&ion of fig. 9. magnified. pith is various in different plants. Inftead of being inA A, The fkin, with its veffels. creafed every year like the wood, it is annually dimiB B B B, The bark. The round niihed, its veffels drying up, and affuming the appearance, holes, C C C, <bc. are the and ftrudture of wood; in fo much that in old trees there lymph-dudts of the bark. is fearce fuch a thing as pith to be difcerned. All the other holes are lit- A ring of fap-veffels ape ufually placed at the outer, edge of the pith, next the wood. In the pine, fig, and . tie cells and fap-veffels. D D D, Parenchymatous infer- walnut, they are very large. The parenchyma of the tions from the bark, with pith, is compofed of fmall cells or bladders, of the fame, kind with thofe of the bark, only of a larger fize. The tire cells, <bc. E E E E, The rays of the wood, general figure of thefe biadders is circular; though in in which the holes are the feme plants, as the thiftle, and borage, they are angular.. air-veffels. Though the pith is originally one connedted chain of bladders ; yet as the plant grows old, they ftrrivel, and N. B. This root has no pith. open in different diredions. In the walnut, after a certain age, it appears in the form of a regular tranfverfeSect. III. Of the Trunks Stalk, or Stem. hollow divifion. In feme plants, it is altogether wantIn deferibing the trunks of plants, it is neceffary to ing ; in others, as the fenchus, nettle, fyc. there is only prerqife, that whatever is faid-with regard to them, ap- a tranfverfe partition of it at every joint. Many other varieties might be mentioned ; • but thefe-muft be left to plies equally to the branches, The trunk, like the root, confifts of three parts, viz. the cbfervation of the reader,.'. the bark, wood, and pith. Thefe parts, though fubftantially the ^fame in the trunk as in the root, are in Plate V. Fig. 1. A tranfverfe fedtion of . a branch of afh, as it appears many.cafes very different in their texture and appearance. ' to the eye.r . The fkin of the bark is compofed of very minute bladders, incerfperfed with longitudinal woody fibres, as Fig. 2. The fame fedtion magnified. in the nettle, thiille, and moft herbs. The outfide of the A A, The bark. fkin is vifibly porous in feme plants, particularly the cane. B B B, An arched ring of fapveffels next the Ikin. The principal body of the bark is compofed of pulp or parenchyma, and innumerable veffels much larger than C C C, The parenchyma, of the.: thofe of the fkin. The texture of the pulpy part, tho’ bark with its cells, and another arched ring of lap-yejfthe fame fubftance with the parenchyma in roots, yet feldom appears in the form of rays running towards the pith ; and when thefe rays do appear, they do not exS D, A 1 circular line of lymphtend above half way to the circumference. The veffeis. dudis immediately below the gf the bark are very differently fituated, and deftined for above arched ring, various purpofes in different.plants. For example, in the E E, The wood. bark of the Pine, the inmoft are lymph-dufts, and exF, The firft year’s growth. ceedingly fmall; the outmofl are gum or refinifc rods vefG, The fecond. H,. The
