72 



MORPHOLOGY OF STEMS. 



as shown in Fig. 127. It is partly owing to this connection of 

 these fibres with the rind that the latter is not separable from 

 the stem. In some Palms, and in Grasses, 

 there is no marked distinction between 

 the wood and rind, or no proper rind at 

 all. In others, such as the Palmetto 

 (Fig. 126), there is a marked rind 

 or false bark, .which receives independent 

 fibro- vascular bundles from the leaf-stalks, 

 and is traversed by them in parallel lines. 

 In Grass-stems, and others with long inter- 

 nodes and closed nodes, the fibro-vascular 

 bundles all run approximately straight 

 and parallel through the internodes, but are 

 intricate and anastomosed in the nodes. 

 The whole centre of the internodes, when 



not hollow or before it becomes so, is occupied by a true pith, 

 like that of an Exogen, and in somecases equally destitute of 

 fibro-vascular bundles, but often with scattered ones, after the 

 manner of certain Exogens anomalous in this respect, such as 

 Nyctaginacese and some Araliaceae. Endogenous stems of 

 simpler structure, as in herbaceous Liliaceae, Commelynaceae, 

 &c., have a distinct cortical portion (at least in the root-stock 

 or portion of stem properly comparable with palm-trunks and 

 the like) ; but this is mostl}' destitute of fibro-vascular bundles. 

 Most of them have two kinds of vascular bundles, one 

 of which not rarely occupies an exact circle in the line of 

 division between the cortical and medullary portion (between 

 bark and pith), and the other is within this circle, either of 

 very few and scattered bundles, as in Convallaria majalis, or 

 numerous and scattered, as in Uvularia and the leafy stems of 

 Tradescantia Virginica ; or these bundles are few and arranged 

 nearly in an inner circle close around the centre. Finally, Luzula 

 and Croomia have only one kind of bundles, answering to the 

 outer ones of Convallaria ; in other words, the woody system 

 forms a simple circle, dividing a purely cellular medullary from a 

 similar cortical portion, thus closely imitating an herbaceous 

 exogenous stem of the same age. 



138. An annual endogenous stem increases in diameter by 

 general growth until it attains its limit. Ligneous and enduring 

 stems increase similarly up to a certain period. Then the rind 



PIG. 127. Diagrammatic view of the curved course of the fibro-vascular bundles 

 ill a palm-trunk. 



