144 



SCIENCE OF GARDENING. 



Part 11. 



Biuls are composed externally of a number of spoon-shaped 

 scales overlapping one another, and converging towards a point 

 ia the apex, and often cemented together hy means of a gluti- 

 nous or mucUaginous substance exuding from their surface. If 

 these scales are stripped off and dissected under the microscope, 

 they will be found to consist, like the leaves or divisions of the 

 calyx, of an epidermis enclosing a pulp interspersed with a net- 

 Avork of fibres, but unaccompanied with longitudinal threads. 

 If the scales of a leaf-bud are taken ajid stripped olF, and the 

 remaining part carefiilly opened up, it will be found to consist 

 of the rudiments of a young branch terminated bv a bunch of 

 incipient leaves imbedded in a white and cottony down, being 

 minute but complete in all their parts and proportions, and 

 folded or rolled up in the bud in a peculiar and determinate 



Bttlhs, which are either radical or caulinary, exliibit 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 tlower, peculiar to their 

 spepies. 



The -pro-pago, which is a sunple gem, pecuUar to some genera 

 of imperfect plants, and exemplified by Gaertner in the lichens, 

 consists of a small and pnlpy mass forming a granule of no regu- 

 lar shape, sometimes naked, and sometimes covered with an 

 envelope, which is a fine epidermis. 



The goiigijlus, wliich is also a simple s^m pecuUar to some 

 genera of imperfect plants, and exemplified by (jaertner in the 

 fuci, consists of a sUghtly indurated ])ulp moulded into a small 

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

 witli an epidermis. 



613. The term caudex, in its present application, is to be understood as including the whole mass or body 

 both of the trunk and root, as distinct from the temporary parts of the plant, or parts already investi- 

 gated ; and as comprehending both the caudex ascendens, and caudex desccndens of Linna;us, or the 

 trunk and its divisions, with the root and its divisions. In opening up and dissecting the caudex, whether 

 ascending or descending, the dissector will soon discover that its internal structure, like its external aspect 

 or habit, is materially different in different tribes of plants. 



614. llie 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 libre,which forms the principal body of the caudex, and becomes some- 

 what indurated with age, though not v/oody, without discovering any further 

 variety of component parts. This, Mirbel observes, is the simplest mode of 

 internal structure existing among vegetables ; it is exemplified in the lower 

 orders of frondose and imperfect plants, particularly the alga? and fungi. 



615. The second general mode of internal structure of the caudex is that in 

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

 substances, totally heterogeneous in their character. A very common va- 

 riety of this mode is that in which an epidermis or bark encloses a soft and 

 inUinj 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 manner characteristic of a tribe or genus. This mode pre- 

 vails chiefly in herbaceous and annual or biennial plants, {fig. 48.) 

 pulp being solid, as in apsidium filix-mass, and tubular, as in the garden 

 parsnep or common hemlock. A second variety of this mode is that in which 

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

 or st ver:il sucli ciiTular and concentric layers, interwoven with thin transverse and 

 divergent layers of pulp, so as to form a firm and compact cylinder, in the centre of 

 which is lodged a pulp or pith. This mode is best exemplified in trees and slirubs 

 {fig. 49.), though it is also applicable to many plants whose texture is chiefly or 

 almost wholly lierbaceous, forming as it were the connecting link between such 

 plants as are purely herbaceous on the one hand, and sucli 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 imperfect in the root of the beet, the common bramble, and burdock j 

 and perfect in the oak or alder. 



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

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

 organs that have been already describecL 



Sect. II. Co7n])osite Organs. 



6] 7. From the preceding analysis, it appears the decomposite organs are reducible to 

 one or other of the several following substances, namely, epidermis, pulp, pith, cortical 

 layers, ligneous layers, and vegetable fibre. These now remain to be further analysed, under 

 the title of composite organs, as being still compound, with a view to reach the ultimate 

 and elementary organs of the vegetable subject. 



618. 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 throughout. In the root and trunk it is a 

 tough and leathery membrane, or it is a crust of considerable thickness, forming a notable portion of the 

 bark, and assuming some peculiar shade of color ; while in the leaves, flowers, and tender shoots, it is a 

 fine, colorless, and transparent film, when detached; and when adherent, it is always tinged with some 

 peculiar shade, which it borrows from the parts immediately beneath it. Du Hamel, Saussure, Hedwig, 

 Comparetti, Bauer, and others, have examined the epidermis, and, according to their descriptions, it is 

 represented as consisting of at least two if not more layers, which in the stem of many plants, are very 

 easily distinguished, particularly in that of the paper-birch, the bark of which may, perhaps, be regarded 

 as a succession of individual cuticles. 



619. The pulp is a soft and juicy substance, constituting the principal mass of succulent plants, and a notable 

 proportion of many parts even of woody plants. It constitutes the principal mass of many of the fungi and 

 fuci, and of herbaceous plants in general. Of those phytologists who have described the pulp, Mirbel is con- 

 sidered the most accurate. He compares it to clusters of small and hexagonal cells or bladders, con- 

 taining for the most part a colored juice, and formed apparently of the foldings and doublings of a fine 

 and delicate membrane, in which no traces of organisation are to be distinguished. In the trunk of what 

 are called dicotyledonous plants, he regards the pulp, or cellular tissue, as consisting of two distinct 

 portions, which he designates by the respective appellations of the herbaceous tissue, and the parenchyma. 

 The former is the exterior portion of the cellular tissue, of which the cells always contain a resinous and 

 colored juice, that communicates its peculiar tinge to the epidermis. The latter is the interior portion of the 

 tissue, composed also of cells, but differing from those of the herbaceous tissue in containing only a 

 watery juice without color, because it has not been exposed to the action of the light, though in the calyx 

 and fruit this watery juice is said to be also often colored. But in the description of the vegetable pulp, 

 the only distinction necessary to be made is that by which it is divided into two parts, namely, an 

 apparatus of hexagonal cells or vesicles, and a contained juice, whether colorless or colored, the union of 

 which substances forms a true pulp. 



