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INDOCTI DIS CANT, ET A MENT ME MINISSE PERITI.
E DIN BURG H.
P L A
tute of sense and spontaneous motion, adhering to and Malpighi have given the name of jeminal root; beanother body in such a manner as to draw from it its cause, by means of it, the radicle and plume, before nourishment, and having a power of propagating itself they are expanded, derive their principal nourishment. by feeds.
The plume, bud, or germ (fig. 3.), is inclosed in two Plate The vegetation and economy of plants is one of those small corresponding cavities in each lobe. Its colour CCCXCIV subjects in which our knowledge is extremely circum- and consistence is much the same with those of the rascribed. A total inattention to the structure and eco- dicle, of which it is only a continuation, but having a nomy of plants is the chief reason of the small progress quite contrary direction; for the radicle descends into that has been made in the principles of vegetation, and the earth, and divides into a great number of smaller of the instability and Auctuation of our theories con- branches or filaments; but the plume ascends into the cerning it; for which reason we shall give a short de- open air, and unfolds itself into all the beautiful va. scription of the structure of plants, beginning with the riety of ftem, branches, leaves, flowers, fruit, &c. The feed, and tracing its progress and evolution to a state of plume in corn shoots from the smaller end of the grain, maturity.
and among maltīters goes by the name of acrospire. 1. Of Seeds.] The seeds of plants are of various The next thing to be taken notice of is the substance figures and sizes. Most of them are divided into two or parenchymatous part of the lobes. This is not a lobes ; though some, as those of the cress-kind, have mere concreted juice, but is curiously organized, and fix; and others, as the grains of corn, are not divided, consists of a vast number of small bladders resembling but entire.
those in the pith of trees (fig. 4.) But as the essential properties of all seeds are the Besides the coats, cuticle, and parenchymatous parts, fame, when considered with regard to the principles of there is a substance perfectly diftinct from these, diftrivegetation, our particular descriptions shall be limited buted in different proportions through the radicle, plume, to one feed, viz. the great garden-bean. Neither is the, and lobes. This inner substance appears very plainly in choice of this seed altogether arbitrary; for, after it be- a transverse section of the radicle or plume. Towards gins to vegetate, its parts are more confpicuous than the extremity of the radicle it is one entire trunk; but many others, and consequently better calculated for in- higher up it divides into three branches ; the middle vestigation.
one runs directly up to the plume, and the other two This seed is covered with two coats or membranes. pass into the lobes on each side, and spread out into a The outer coat is extremely thin, and full of pores; great variety of small branches through the whole bobut may be easily separated from the inner one (which dy of the lobes (fig. 4.) This substance is very pro
Plate is much thicker), after the berimbas been boiled, or lain perly termed the seminal root: for when the feed is fown, cccxci. a few days in the soil. At the thick end of the bean the moisture is first absorbed by the outer coats, which
there is a small hole visible to the naked eye, immedi- are everywhere furnished with fap and air-vessels; from Platcately over the radicle or future root, that it may have these it is conveyed to the cuticle ; from the cuticle it CCCXCIV a free passage into the foil (fig. 1. A). When these proceeds to the pulpy part of the lobes ; when it has
coats are taken off, the body of the feed appears, which got thus far, it is taken up by the mouths of the small
which communicates both with the plume and radicle,
capital branches, one of which is inserted into each promotes the growth and expansion of that organ; and Plate
lobe, and sends off smaller ones in all directions through part of it descends into the radicle, for nourishing and CCCXCI. the whole fubstance of the lobes (fig. 4. AA). These evolving the root and its various filaments. Thus the
ramifications become so extremely minute towards the 'plume and radicle continue their progress in oppofite di.
Plant. It is here worth remarking, that every plant is really renchymatous part of the radicle, but greatly augment
possessed of two roots, both of which are contained in ed. The bark is of very different sizes. In molt trees
sels are not pervious, so as to communicate with each These dissimilar leaves defend the young plume from other; but consist of distinct little cells or bladders, the injuries of the weather, and at the fame time, by scarcely visible without the aslistance of the microscope. absorbing dew, air, &c. assist the tender radicle in nou In all roots, these cells are constantly filled with a thin rishing the plume, with which they have still a connec. watery liquor. They are generally of a spherical figure; tion by means of the seminal root above described. But though in some roots, as the buglofs and dandelion, they when the radicle or second root has descended deep are oblong. In many roots, as the horse-radish, peony, enough into the earth, and has acquired a sufficient asparagus, potatoe, &c. the parenchyma is of one uninumber of filaments or branches for absorbing as much form itructure. But in others it is more diversified, aliment as is proper for the growth of the plume; then and puts on the shape of rays, running fru• the centre
the seminal or dissimilar leaves, their utility being en towards the circumference of the bark. These rays Plate tirely superseded, begin to decay and fall off.
fometimes run quite through the bark, as in lovage ; CCCXCIV Fig. 1. A, the foramen or hole in the bean through and sometimes advance towards the middle of it, as in which the radicle shoots into the foil.
melilot and most of the leguminous and umbelliferous Fig. 2. A transverse section of the bean ; the dots plants. These rays generally stand at an equal distance being the branches of the seminal root.
from each other in the same plant; but the distance vaFig. 3. A, the radicie. B, the plume or bud. ries greatly in different plants. Neither are they of
Fig. 4. A, a longitudinal section of one of the lobes equal fizes: in carrot they are exceedingly small, and of the bean a little magnified, to show the small bladders scarcely discernible ; in melilot and chervil, they are of which the pulpy or parenchymatous part is compo- thicker. They are likewise more numerous in fome plants sed.
than in others. Sometimes they are of the same thickFigs. 5. 6. A, a transverse section of the radicle. B, ness from one edge of the bark to the other; and some a transverse fection of the plume, thowing the organs or grow wider as they approach towards the skin. The vesels of the seninal root.
vessels with which there rays are amply furnished, are Plate Fig. 4. A view of the feminal root branched out up- supposed to be air-vesels, because they are always found CCCXCI. . on the lobes.
to be dry, and not fo transparent as the vessels which Plate Fig. 7. The appearance of the radicle, plume, and se- evidently contain the sap. CCCXCIV minal root, when a little further advanced in growth. In all roots there are ligneous vefsels dispersed in dif
Havir.g thus briefly described the feed, and traced its ferent proportions through the parenchyına of the bark. evolution into three principal organic parts, viz. the These ligneous vessels run longitudinally through the plume, radicle, and feminal leaves, we shall next take an bark in the form of small threads, which are tubular, as anatomical view of the root, trunk, leaves, &c.
is evident from the rising of the sap in them when a
stance they have got the name of lymph-dues.
Plant. milky glutinous lymph, as in the angelica, sonchus, The trunk, like the root, consists of thrce parts, viz. Plane.
burdock, scorzonera, dandelion, &c. The lymph-ducts the bark, wood, and pith. These parts, though sub-
bladders, interspersed with longitudinal woody fibres,
though the fatne fubftance with the parenchyma in
appear, they the bark or pith. It consists of two distinct substances, do not extend above half way to the circumference. viz. the pulpy or parenchymatous, and the ligneous. The vessels of the bark are very differently situated, and The wood is connected to the bark by large portions of defined for various purposes in different plants. For the bark inserted into it. These insertions are mostly in example, in the bark of the pine, the inmost are lymph the form of rays, tending to the centre of the pith, which ducts, and exceedingly small; the outmost are gum or are easily discernible by the eye in a transverse section of refiniferous vessels, destined for the secretion of turpenmost roots. These insertions, like the bark, contist of tine; and are so large as to be distinctly visible to the many vessels, mostly of a round or oval figure.
The ligneous vefsels are generally disposed in collateral The wood lies between the bark and pith, and conrows running longitudinally through the root. Some fists of two parts, viz. a parenchymatous and ligneous. of these contain air, and others fap. The air-vessels are In all trees, the parenchymatous part of the wood, so called, because they contain no liquor. These air- though much diversificd as to fize and consistence, is univessels are distinguished by being whiter than the others. formly disposed in diametrical rays, or insertioits run.
The pith is the centrical part of the root. Some ning betwixt similar rays of the ligneous part. roots have no pith, as the stramonium, nicotiana, &c.; The true wood is nothing but a congeries of old dried others have little or none at the extremities of the roots, lymph-ducts. Between the bark and the wood a new but have a confiderable quantity of it near the top. The ring of these ducts is formed every year, which gradupith, like every other part of a plant, is derived from ally loses its softness as the cold season approaches, and the seed; but in some it is more immediately derived towards the middle of winter is condensed into a solid from the bark: for the insertions of the bark running ring of wood. These annual rings, which are distinctly in betwixt the rays of the wood, meet in the centre, and visible in most trees when cut through, serve as natural constitute the pith. It is owing to this circumstance, marks to distinguish their age (fig. 10. 11.) The rings Plate that, among roots which have no pith in their lower of one year are sometimes larger, sometimes lels, than CCCXCV parts, they are amply provided with it towards the top, those of another, probably owing to the favourableness as in columbine, lovage, &c.
or unfavourableness of the season. The bladders of the pith are of very
different sizes, The pith, though of a different texture, is exactly of
We Thall conclude the description of roots with ob ture of wood; infornuch that in old trees there is scarce
walnut, they are very large. The parenchyma of the Place
Fig. 8. A transverse section of the root of worm- pith is composed of small cells or bladders, of the same CCCXCIV wood as it appears to the naked eye.
kind with those of the bark, only of a larger size. The
3. Of the Trunk, Stalk, or Stem.] In describing the gether wanting; in others, as the fonchus, nettle, &c.