10

THE PALM-STEM.

the stem of which the vascular bundles entering the leaves have the aspectof medullary rays. The crossing is also very evident in the stem of Pandanus,Dracaena Draco, Aletris fragrans, Aloe, Bambma, &c.

Obs. 2. The smaller diameter of the lower liber-like end of the vascularbundles simply explains the less degree of thickness of the fibrous layer ofthe stem. Where each vascular bundle ends in a single filament, as inBadris, Geonoma, lepidocaryum, Calamus, Kunthia, (Enocarpus, Hyospathe,Bdiapis, &c., this layer is very thin; when, on the other hand, the vascularbundle gives off several fibres, or when, as in Mauritia vinifera, the fibresretain a considerable thickness, the thickness of the fibrous layer is notaltogether inconsiderable. I found it in Leopoldinia pulchra from ^ to 2lines; in Byagrus cocoides 1 line; in Cocos nucifera , Euterpe edulis, Mauritiavinifera, 6 lines thick.

The Cellular Tissue of the Palm-stem.

The cellular tissue is not, as iu Dicotyledons , distri-buted into distinct bark, pith, and medullary rays, sincethe vascular bundles are scattered throughout the wholesubstance of the stem. Nevertheless, the cellular tissueexhibits different forms in the different layers of the stem,which may in many respects be compared with the formsof the cells of the bark, pith, and medullary rays.

The form of the cellular tissue in Palm-stems in generalpossesses 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, notoidy in different species, but in different layers of thesame stem. In general, these cells are only of a mediumsize, and apparently in all species, at a certain period ofvegetation, densely filled with starch.

In the fibrous layer, the cellular tissue is composed ofsmall, thin-walled cells, mostly expanded transversely,between which are small intercellular passages. In youngstems, 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 formationssubsequently disappear. The cells of this layer only