10 THE PALM-STEM. 



the stem of which the vascular bundles entering the leaves have the aspect 

 of medullary rays. The crossing is also very evident in the stem viPandanus, 

 Dracaena Draco, Aletris fragrans, Aloe, Bambusa, &c. 



Obs. 2. The smaller diameter of the lower liber-like end of the vascular 

 bundles simply explains the less degree of thickness of the fibrous layer of 

 the stem. Where each vascular bundle ends in a single filament, as in 

 Bactris, Geonoma, Lepidocaryum, Calamus, Kunthia, (Enocarpus, Hyospathe, 

 Rhapis, &c., this layer is very thin ; when, on the other hand, the vascular 

 bundle gives off several fibres, or when, as in Mauritia vinifera, the fibres 

 retain a considerable thickness, the thickness of the fibrous layer is not 

 altogether inconsiderable. I found it in Leopoldinia pulchra from ^ to 2 

 lines ; in Syagrus cocoides 1 line ; in Cocos nucifera, Euterpe edulis, Mauritia 

 mnifera, 6 lines thick. 



The Cellular Tissue of the Palm-stem. 



The cellular tissue is not, as in Dicotyledons, distri- 

 buted into distinct bark, pith, and medullary rays, since 

 the vascular bundles are scattered throughout the whole 

 substance of the stem. Nevertheless, the cellular tissue 

 exhibits different forms in the different layers of the stem, 

 which may in many respects be compared with the forms 

 of the cells of the bark, pith, and medullary rays. 



The form of the cellular tissue in Palm-stems in general 

 possesses but one definite character, namely, it is paren- 

 chymatous, and its cells are usually arranged in perpen- 

 dicular rows, the forms of these cells varying much, not 

 only in different species, but in different layers of the 

 same stem. In general, these cells are only of a medium 

 size, and apparently in all species, at a certain period of 

 vegetation, densely filled with starch. 



In the fibrous layer, the cellular tissue is composed of 

 small, thin -walled cells, mostly expanded transversely, 

 between which are small intercellular passages. In young 

 stems, the cortical layer of which is still in full vegetation, 

 chlorophyll-granules are found in the outer cells, starch- 

 granules in those lying deeper ; the granular formations 

 subsequently disappear. The cells of this layer only 



