214 



SCIENCE OF AGRICULTURE. 



Part II. 



1348. The plumule (a), the future plant in miniature, is the interior and essential portion of the embryo, 

 and seat of vegetable life. In some seeds it is so minute as to be scarcely perceptibly ; while in others it 

 is so large as to be divisible into distinct parts, as in the garden bean. 



1349. The pericarp, which in different species of fruit assumes so many varieties of contexture, acquires 

 its several aspects, not so much from a diversity of substance as of modification. 



1350. The valves of the capsule, but particularly the partitions by which it is dividc-d into cells, are com- 

 posed of a thin and skinny membrane, or of an epidermis covering a pulp more or less indurated, and 

 interspersed with longitudinal fibres. The capsule of the mosses is composed of a double and netlike 

 membrane, enclosed within a fine epidermis. 



1351. The pome is composed of a fine but double epidermis, or, according to Knight, of two skins, enclos- 

 ing a soft and fleshy pulp, with bundles of longitudinal fibres passing through it, contiguous to, and in the 

 direction of, its longitudinal axis. 



1352. The valves qf the legume are composed of an epidermis enclosing a firm but fleshy pulp lined for 

 the most part with a skinny membrane, and of bundles of longitudinal fibres forming the seam. 



1353. Tlie nutshell, whether hard and bony, or flexible and leathery, is composed of a pulp more or less 

 highly indurated, intersijersed with longitudinal fibres, and covered with an epidermis. 



1354. The drupe is composed of an epidermis enclosing a fleshy pulp, which is sometimes so interwoven 

 with a multiplicity of longitudinal fibres as to seem to consist wholly of threads, as in the cocoa-nut. 



1355. The berry is composed of a very fine epidermis enclosing a soft and juicy pulp. 



1356. The scales of the strobile are composed of a tough and leathery epidermis, enclosing a spongy but 

 often highly indurated pulp interspersed with longitudinal fibres that pervade also the axis. 



1357. The flower-stalk, or peduncle supporting the flower, which is a prolongation of the stem or branch, 

 or rather a partial stem attached to it, if carefully dissected with the assistance of a good glass, will be 

 found to consist of the following parts : 1st, An epidermis, or external envelope ; 2dly, A paren- 

 chyma, or soft and pulpy mass ; 3dly, Bundles of longitudinal threads or fibres, originating in the stem or 

 branch, and passing throughout the whole extent of the parenchyma. The several organs of the flower 

 are merely prolongations of the component parts of the flower-stalk, though each organ does not always 

 contain the whole of such component parts, or at least not under the same modifications. The epidermis, 

 however, and parenchyma are common to them all ; but the longitudinal threads or fibres are seldom, if 

 ever, to be found, except in the calyx or corolla. 



1358. The leaf-stalk, or petiole supporting the leaf, which is a prolongation of the branch or stem, or 

 rather a partial stem attached to it, exhibits upon dissection the same sort of structure as the peduncle, 

 namely, an epidermis, a pulp or parenchyma, and bundles of longitudinal threads or fibres. 



1359. Getns. There exist among the different tribes of vegetables four distinct species of gems, two 

 peculiar to perfect plants, the bud and bulb, and two peculiar to imperfect plants, the propago and gongylus; 

 the latter being denominated simple gems, because furnished %vith a single envelope only ; and the former 

 being denominated compound gems, because furnished with more than a single envelope. 



1360. Bvds are composed externally of a number of spoon- 

 shaped scales, overlapping one another and converging towards 

 a point in the apex, and often cemented together by means of a 

 glutinous or mucilaginous sub.stanoe exuding from their sur- 

 face. If these scales are stripped off and dissected under the mi- 

 croscope, they will be found to consist, Uke the leaves or divi- 

 Kions of the calyx, of an epidermis enclosing a pulp interspersed 

 with a network of fibres, but unaccompanied witli longitudinal 

 threads. If the scales of a leaf-bud are taken and stripped ofF, 

 and the remaining part carefully opened up, it will be found to 

 consist of the rudiments of a young branch terminated by a 

 bunch of incipient leaves embedded in a white and cottony 

 down, being minute but complete in all their parts and pro- 

 portions, and folded or rolled up in the bud in a peculiar and 

 determinate manner. 



1361 . Bulbs, which are either radical or caulinary, exhibit in 

 their external structure, or in a part of their internal structure 

 that is easily detected, several distinct varieties, some being 

 solid, some coated, and some scaly ; but all protruding in the 

 process of vegetation the stem, leaf, and flower, peculiar to 

 their species. 



1362. The propai^o, which is a simple gem, peculiar to some 

 nera of imperfect plants, and exemplified by Gaertner in 

 le lichens, consists of a small and pulpy ma.ss forming a gra- 

 nule of no regular shape, sometimes naked, and sometimes 

 covered with an envelope, \vhich is a fine epidermis. 



1363. The gongylus, which is also a simple gem peculiar to 

 some genera of imperfect plants, and exemplified by Gaertner 

 in the fuel, consists of a slightly Indurated pulp moulded into a 

 small and globular granule of a firm and solid contexture, and 

 invested with an epidermis. 



^; 



183 



1364. The caudex includes the whole mass or body both of the trunk and 

 root ; its internal structure, like its external aspect or habit, is materially dif- 

 ferent in different tribes of plants. 



1365. The first general mode of the internal structure of the caudex is that in 

 which an epidermis encloses merely a homogeneous mass of pulp or slender 

 fibre. This is the simplest mode of internal structure existing among vege- 

 tables : it is exemplified in the lower orders of imperfect plants, particularly j 

 the Algse and JPungi. 



1366. The second general mode of internal structure of the eavdex is that in 

 which an epidermis encloses two or more substances, or assemblages of sub- 

 stances, totally heterogeneous in their character. A very common variety of 

 this mode is that in which an epidermis or bark encloses a soft and pulpy mass, 

 interspersed with a number of longitudinal nerves or fibres, or bundles of 

 fibres, extending from the base to the apex, and disposed in a peculiarity of 



2g,i manner characteristic of a tribe or genus. This mode prevails chiefly in herbaceous 



and annual or biennial plants, {fig. 183.) A second variety of this mode is that in 

 which a strong and often thick bark encloses a circular layer of longitudinal fibres, or 

 several such circular and concentric layers, interwoven with thin transverse and diver- 

 gent layers of pulp, so as to form difirm and compact cylinder, in the centre of which is 

 lodged a pulp or pith. This mode is best exemplified in trees and shrubs {fig. 184.), 

 though it is also applicable to many plants whose texture is chiefly or almost wholly 

 herbaceous, forming as it were the connecting link between such plants as are purely 

 herbaceous on the one hand, and such as are purely woody on the other In the latter 

 case the wood is perfect ; in the former case it is imperfect. The wood being imper- 

 fect in the root of the beet, the common bramble, and burdock ; and perfect in the oak 

 or alder. 



1367. The appendages of the plant, whether conservative or reproductive, exhibit 

 nothing in their internal structure that is at all essentially different from that of the 

 organs that have been already described. 



SuBSECT. 2. Composite Organs. 



1368. The composite organs are the epidermis, pulp, pith, cortical layers, ligneous 

 layers, and vegetable fibre, which may be further analysed, as being still compound, with 

 a view to reach the ultimate and elementary organs of the vegetable subject. 



1369. Structure of the vegetable epidermis. The epidermis of the vegetable, which, from its resemblance 

 to that of the animal, has been designated by the same name, is the external envelope or integument of 

 the plant, extending over the whole surface, and covering the root, stem, branches, leaves, flower, and 

 fruit, with their appendages ; the summit of the pistil only excepted. But although it is extended over 

 the whole surface of the plant, it is not of equal consistence tliroughout. In the root and trunk it is a 



