40 THE PALM-STEM. 



me that a comparison between the stems of the two great 

 classes of vegetables may be instituted without straining 

 the facts. 



Although the vascular bundle belonging to each indi- 

 vidual leaf cannot be distinguished from the rest in the 

 cross section of a Palm-stem since the position in con- 

 centric circles (which should result from the similar 

 course taken by all the vascular bundles going to one 

 leaf) is variously distorted yet we may imagine the 

 vascular bundles going to each leaf united into a tubular 

 layer. This tube, however, is not cylindrical, but forms 

 an elongated cone. As long as the leaf which is supplied 

 by these bundles remains the uppermost, the conical tube, 

 composed of its vascular bundles, forms the most external 

 layer of the stem. But when a new, higher leaf is deve- 

 loped, the vascular bundles going to this leaf form a new 

 layer, which is developed on the outside of the last layer. 

 Since, however, the apices of these conical layers are not 

 closed, but the vascular bundles of which they are com- 

 posed run outward again from the centre of the stem to 

 reach the leaves, the above described crossing results, 

 occurring between the vascular bundles which emerge 

 into a leaf, and all subsequent bundles running up to 

 younger leaves. 



If we compare with this the structure of the first year's 

 shoot of a Dicotyledonous tree, for excellent observations 

 on which we are indebted to Dupetit-Thouars (Histoire 

 d'un morceau de bois), we meet with a very similar 

 course of the vascular bundles. The vascular bundles in 

 it, running to the lowest leaves, which have formed the 

 corona on the lowest part of the branch, and which we 

 will designate A, pass in a curve outwards, and the 

 vascular bundles supplying the next succeeding leaf above 

 (B), lie with their lower portions on the outside of the 

 bundles A, up to the point where these latter turn out- 

 ward ; above this they form the succeeding portion of the 

 corona up to where they also pass outward into the leaf. 

 We see, therefore, that the course of the vascular bundles 



