EXOGENS. 



EXOGENS. 



bundles appear to have a tolerably uniform structure below and in 

 the middle, but toward the upper end the onward developing portion 

 of each older bundle passes into the form of a primary bundle, or, 

 in other words, every primary vascular bundle of a new interuode 

 appears as the immediate prolongation, not of the primary bundle of 

 the preceding internode (which rather runs to a leaf), but of the 

 layer of increase of this, the elementary portions of which do not 

 correspond to any expansion in the longitudinal direction. 



On the literature of this subject Schleiden says " Almost all that 

 has been said by isolated authors is wholly useless, either because 

 they have had no regard to the history of development, or, if they 

 have noticed this, have spoken so indiscriminately of growth, increase, 

 and enlargement, without distinguishing whether new cells have 

 originated, cells already existing expanded, or merely become trans- 

 formed into different tissues by the alteration of the form and 

 configuration of their walls. 



" Two notions there are especially which have long sadly confused 

 our science, from which a correct method would have completely 

 saved us, since both were, at least at the time, and in the species on 

 which they were built up, wholly unfounded fables, having no con- 

 nection with any guiding principles, and consequently never should 

 have assumed scientific perspicuity, much less, as did happen, have 

 served as a temporary basis for theories pervading the whole science 

 of botany. 



" The first is the idea of Desfontaines of the distinction between 

 Monocotyledons and Dicotyledons, that the former develop new 

 structure in the centre of the axis, and grow in the inside (Plantie 

 Endogence), while the latter produce ligneous substance close under 

 the bark, and deposit it on the inner side, and thus grow on the 

 outside (Planta Ktogence). All this had no greater foundation than 

 the fact that in the Monocotyledonous axis the vascular bundles are 

 farther apart in the centre ; consequently, in the preponderance of 

 parenchyma, the substance is more lax. It was not ever attempted 

 to make even a superficial observation of the process of growth ; if it 

 had been merely observed that the vascular bundles going to the 

 lower leaves, consequently the older, crossed those going to the 

 upper leaves, which must be the younger, a child might have been 

 made to understand at once that a growth of new vascular bundles 

 in the interior was an absolute impossibility. Nevertheless, upon 

 this empty fancy, which a child might have refuted, De Candolle 

 built a grand system of vegetables, which it never did require 

 the distinguished and comprehensive researches of Mohl to over- 

 throw. 



" The second notion is that of Du Petit Thouars, which waa not 

 less ill-grounded, which, as expressed by him, would be upset by 

 every even the most superficial observation, and even in its more 

 refined subsequent statement is by no means established, but has 

 important and apparently irresistible objections against it. Du Petit 

 Thouars thought that all increase of thickness of the axis resulted 

 from the descent of roots from the buds. Such a crude notion 

 scarcely required refutation. On the other hand, it was afterwards 

 stated that the formless but organisable subatanc? (the cambium) 

 was gradually organised from the buds downwards. The only 

 possible foundation for this view, namely, evidence obtained by 

 thorough investigation of the history of development, is still due 

 from all its asaertors, the latest, Gaudichaud, Ac., included. There- 

 fore it is already to be set aside as devoid of foundation. But the 

 contrary can be made good, that, in the first place, no cambium ever 

 exist* as a formless fluid in the plant, unless we would so call the 

 cytoblastema inclosed in the cells ; secondly, that, so far as obser- 

 vation at present reaches, cells are always formed in cells, that this 

 cell-formation, according to the observations I have made in the 

 C'aelecr, &c., progresses from below upward; thirdly, that the 

 axillary bud is ah eady formed in the terminal bud before the axis 

 begins to increase in thickness, and that certainly the cells of the bud 

 are organised into vascular bundles from the vascular bundles of the 

 stem upward into the bud, and not in the reverse direction. By 

 these remarks the whole notion seems to me to be for the present set 

 o-side, and it would require quite other support than that which 

 Gaudichaud's imperfect attempts in anatomy and physiology could 

 give it. 



" Lastly, I must notice the most recent views of Martius on the 

 structure of the sterna of palms, &e. Martins asserts that here the 

 v&cular bundles, the primary structure of which is sketched out in 

 the conical terminal bud, on the whole, as I have already explained 

 it ( Wiegmann's 'Archiv.,' 1839, 219), do not merely grow upwards 

 into the leaves, but also downward, by their lower end, in the stem. 

 The facts I must entirely oppose from my own observations. 

 Hitherto I have never had an opportunity of investigating living 

 Palms, or more than small fragments of dead ones. But from what 1 

 saw I believe I may venture to conclude that the stem of Palms does 

 not essentially deviate in such a way from those of other Monocoty- 

 ledons, that one may not transfer to the Palms, in the main points, 

 the laws of structure found there. Now, so far as I know, such a 

 process of growth does not occur in any Monocotyledonous plant. 

 According to my observations the newly-produced vascular bundles 

 merely grow continuously upward. In advancing the distinction of 

 limited and unlimited bundles Martius follows me, but in my opinion 



he has not conceived nearly clearly enough the distinction between 

 developed and undeveloped internodes ; and in particular he has not 

 formed a clear conception of the peculiarities of the stem with undeve- 

 loped internodes, and the conditions of structure resulting therefrom. 

 Moreover he has left the meaning of the term growth (fortwachseu) 

 of a vascular bundle equivocal. If it means that the already existing 

 elongated cells become transformed into vascular bundles, it describes 

 no peculiar process of growth the vascular bundles were already to 

 be distinguished in their elementary condition ; but if it means that 

 the cells themselves, of which the vascular bundles are composed, are 

 produced subsequently, originating above first and proceeding down- 

 wards, this is I believe erroneous. It is necessary to bear in mind 

 the essential distinction between monocotyledonous axes with and 

 without a cambium circle, in order to understand these structures. 

 Where no cambium exists there are no other new cells formed besides 

 those in the point of the bud ; but where there is cambium, all deve- 

 lopment, and so also the development of new vascular bundles in the 

 stem, proceeds upwards and outwards ; never, so far as I have been 

 able to observe, downwards or towards the interior. The lowest and 

 innermost cells are always the oldest, never the upper or outer (of 

 course excluding the bark, to which alone an endogenous growth can 

 be ascribed). I must therefore distinctly assert that in the Palms, as 

 in all Monocotyledons, the lower end of an older vascular bundle never 

 reaches down into an internode lower than that in which the lower 

 end of its first rudiment originated." 



The following is a summary of the nature of axial structures, 

 and the names given to the various parts of which they aro 

 composed : 



1. Duration. 



A. Annual. Stem (Caulis). 



Internodes (Internodia). 

 a. Only existing in the beginning of the period of vegetation, 



fugacious (Internodia fugacia). 

 1. Enduring the whole period (Internodia, annua). 

 c. Only existing in the latter part of the period of vegetation 



(Internodia serotina). 



B. Perennial. Trunk (Truncui). 



2. Position on the Soil. 



A. Above ground (Epigaus). 



B. Under ground (llypogteus). 



3. Form. 



A. Developed Internodes (Internodia elongata). 



B. Undeveloped Interuodes (Internodia abbreviata). 



C. Disciform expanded Internodes (Internodia discifvrmia). 



D. Concavely expanded Internodes (luternodia concava). 



N.B. Rigid, pointed, leafless, or defoliated Internodes are called 

 Spines (Spince) ; soft, curling, and thus climbing round foreign 

 objects, Tendrils (Cirrhi, Capreoli). 



4. Various Internodes of the same Axis. 



A. Bearing true Leaves and Branches (Caulis and Truncus). 



N.B. Sometimes no leaves are developed (Axis aphyllui), or 

 they fall off from the truncus, mostly at the end of the first year 

 (Axit denudatus). The stem may grow out from the terminal 

 bud of an embryo, as in the simple stem, or out of a trunk. A 

 stem produced from a trunk might be called Scapus ; but this id 

 a wholly superfluous term. 



B. Bearing only bracts, bracteoles, or flowers, Peduncle (Pedunculi) ; 



in a compound inflorescence the internode bearing a single flower 

 is called the Pedicel (Pedicellus). Receptaculmn is a superfluous 

 expression in the Synanthere<e. Pedunculus disciformis, conicus, 

 &c., is simpler and more correct. Also in Ficus, Ped'.mculus 

 concavus. 



C. Internodes between calyx and pistil, Receptacle (Torus), e. g. in somo 



Rosacece, Torus disciformis (in PotentMa), Torus concavtis (in Rosa). 



a. Interuodes between calyx and stamens (e. g. in Rubus), or calyx 



and corolla (e. g. in Passiflora), the Disc (Discus), e. g. plcmus (iu 

 (ieum), D. tubidosus (in Cereus grandiflorus). 



b. Intel-nodes between corollaand stamens,Androphore (Andropliorum), 



e. g. A. eloiiyatitm (in C'leome). 



c. Interuodes between stamens and pistil, Gynophore (Gynophorum), 



e. g. 0. conicum (in Rubus). 



D. Intel-nodes between calyx and sead-buda, as a hollow disc inclosing 



the seed-buds, Inferior Germeu (German inferum), e. g. in Synan- 

 therae, Orchidacece. 



E. Internodes between stamens and seed-buds, as a plate with the 



bordT3 curved inward together, in the cavity of which tho 

 seed-buds occur, Stalk-Pistil (Pistillum cauligenum). In Liliacece 

 and Leguniinosce ( ? ). 



P. End of the stalk in the germen, as support of the seeds, Spermo- 

 phore (Spcrmopliorum), in Seed-Buds (Qcmmula). (For the parts, 

 of these see below, under the Seed-Bud). 

 5. As to the Nodes. 



A. With Imperfect Nodes (Caulis, Truncus). 



B. With Perfect Nodes. 

 a. Stalk (C-idmns). 



I. Stem (Calamus). 



