Page:Encyclopædia Britannica, first edition - Volume I, A-B.pdf/61

 A G R I C U The outer coat is extremely thin, and full of pores ; but may be eafily feparated from the inner one, (which is much thicker), after the bean has been boiled, or lain • a few days in the foil. At the thick end of the bean, there is a fmall hole vilible to the naked eye, immediately over the radicle or future root, that it may have a free paffage into the foil. Plate IV. fig. i. A. When thefe coats are taken off, the body of the feed appears, which is divided into two fmooth portions or lobes. The fmoothnefs of tire lobes is owing to a thin'film or cuticle with which they are covered. At the bafrs of the bean is placed the radicle or future root, Plate IV. fig. 3. A. The trunk of the radicle, juft as it enters into the body of the feed, divides into two capital branches, one of which is inferred into each lobe, and fends off fmaller ones in all direftions through the whole fubftance of the lobes, Plate IV. fig. 7. A A. Thefe ramifications become fo extremely minute towards the edges of the lobes, that they require the fineft glaffes to render them vifible. To thefe ramifications Grew and Malpighius have given the name of feminal root; becaufe, by means of it, the radicle and plume, before they are expanded, derive their principal nouriftiment. The plume, bud, or germ, Plate IV. fig. 3. is inclofed in two fmall correfponding cavities in each lobe. Its colour and confiftence is much the fame with thofe of the radicle, of which it is only a continuation; but having a quite contrary direction: For the radicle defcends into the earth, and divides. into a great number of fmaller branches or filaments ; but the plume alcends into the open air, and unfolds itfelf into all the beautiful variety of ftem, branches, leaves, flowers, fruit, 6'c. The plume in com ftioots from the fmaller end of the grain, and, among maltfters, goes by the name of acrofpire. The next thing to be taken notice of is the fubftance, or parenchymatous part of the lobes. This is not a mere concreted juice, but is curioufly organifed, and confifts of a vaft number of fmall bladders refembling thofe in the pith of trees, Plate IV. fig. 4. Befides the coats, cuticle, and parenchymatous parts, there is a fubftance perfectly diftihft from thefe, diftributed in different proportions through the radicle, plume, and lobes. This inner fubftance appears very plainly in a tranfverfe feftion of the radicle or plume. Towards the extremity of the radicle, it is one entire trunk ; but higher up, it divides into three branches.; the middle one runs direcftly up to the plume, and the other two pafs into the lobes on each fide, .and fpread out into a great variety of fmall branches through the whole body of the lobes, .Plate IV. fig. 7. This fubftance is very properly termed the feminal root: for when the feed is fown, the moifture is firft abforbed by the outer coats, which are every where furniflied with fap and air-veffels; from thefe it is conveyed to the cuticle; ’ from the cuticle it proceeds to the pulpy part of the lobes ; when it has got thus far, it is taken up by the mouths of the fmall branches of the feminal root, and paffes from one branch into another, till it is all collefteft into the main trunk, which communicates both with the plume and radicle, the two principal involved organs of the future plant. After this the fap, or vegetable food, runs in two oppoVol.I. No.2.

L T U R E. , 41 fite diredtions ; part of it afcends into the plume, and promotes the growth and expanfion of that organ ; and part of it Jefcends into the radicle, for nourifhing and evolving the root and its various filaments. Thus the plume and radicle continue their progrefs in oppofite directions, till the plant arrives at maturity. It is here worth remarking, that every plant is really pofleffed of two roots, both of which are contained in the feed. The plume and radicle, when the feed is firft depofited in the earth, derive their nouriftiment from the feminal root: but, afterwards, when the radicle begins to ftioot out its filaments, and to abforb fome moifture, not, however, in a fufficient quantity to fupply the exigencies of the plume, the two lobes, or main body of the feed, rife along with the plume, aflume the appearance of two leaves, refembling the lobes of the leed in fize and ftiape, but having no refemblance to thofe of the plume, for which reafon they have got the name of dijjimilar leave's. Thefe, diflimilar leaves defend the young plume from the injuries of the weather, and at the fame time, by abforbing dew, air, <bc. aflift the tender radicle in nouriftiing the plume, with which they have ftill a connection by means of the feminal root above defcribed. But, when the radicle or fecond root has defcended deep enough into the earth, and has acquired a fufficient number of filaments or branches for abforbing as much aliment as is proper for the growth of the plume; then the feminal, or diflimilar leaves, their utility being entirely fuperfeded, begin to decay and fall off. Plate IV. Fig. j. A, The foramen, or hole in the bean through which the radicle ftioots into the foil. Fig. 2. A tranfverfe fedlion of the bean ; the dotes being the branches of the feminal root. Fig. 3. A, The radicle. B, The plume or bud. Fig. 4. A, A longitudinal fe&ion of on,e of the lobes of the bean a little magnified, to ffiow the final! bladders of which the pulpy or parenchymatous.part is compofed. Fig. 5, 6. A, A tranfverfe feclion of the radicle. B, A tranfverfe fe&ion of the plume, ffiowing the organs or veffels of the feminal root. Fig. 7. A, A view of the feminal root branched out upon the lobes. Fig. 8. The appearance of the radicle, plume, and feminal root, when a little further advanced in growth. Having thus briefly defcribed the -feed, and traced its evolution into three principal organic parts, viz. the plume, radicle, and feminal leaves, we ffiall next take an anatomical view of the root, trunk, leaves, <bc. L Sect.