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THE PALM-STEM.

me that a comparison between the stems of the two greatclasses of vegetables may be instituted without strainingthe facts.

Although the vascular bundle belonging to each indi-vidual leaf cannot be distinguished from the rest in thecross section of a Palm-stem—since the position in con-centric circles (which should result from the similarcourse taken by all the vascular bundles going to oneleaf) is variously distorted—yet we may imagine thevascular bundles going to each leaf united into a tubularlayer. This tube, however, is not cylindrical, but formsan elongated cone. As long as the leaf which is suppliedby these bundles remains the uppermost, the conical tube,composed of its vascular bundles, forms the most externallayer of the stem. But when a new, higher leaf is deve-loped, the vascular bundles going to this leaf form a newlayer, which is developed on the outside of the last layer.Since, however, the apices of these conical layers are notclosed, but the vascular bundles of which they are com-posed run outward again from the centre of the stem toreach the leaves, the above described crossing results,occurring between the vascular bundles which emerge _into a leaf, and all subsequent bundles running up toyounger leaves.

If we compare with this the structure of the first year’sshoot of a Dicotyledonous tree, for excellent observationson which w r e are indebted to Dupetit-Thouars (Idistoired’un morceau de hois), we meet with a very similarcourse of the vascular bundles. The vascular bundles init, running to the lowest leaves, which have formed thecorona on the lowest part of the branch, and which wewill designate a, pass in a curve outwards, and thevascular bundles supplying the next succeeding leaf above(b), lie with their lower portions on the outside of thebundles a, up to the point where these latter turn out-ward ; above this they form the succeeding portion of thecorona up to where they also pass outward into the leaf.IVe see, therefore, that the course of the vascular bundles