20 THE PALM-STEM. 



the stem are also in a less crowded condition than in the 

 two preceding forms. Partly by this, and partly by the 

 smaller amount of decrease of the liber in the middle of 

 the stem, is explained the more uniform hardness of the 

 different layers of the latter. 



The vascular bundles of Calamus exhibit a very pecu- 

 liar structure. The liber is here also strongly developed 

 in the outer layer of the stem, but the woody portion 

 displays this peculiarity, that, disregarding rare excep- 

 tions, instead of several large vessels, it contains only 

 one of unusual dimensions, occupying the centre of the 

 bundle. Behind this large vessel (except in the outer- 

 most vascular bundles) lie small spiral vessels. The cells 

 of the woody portion have thick walls, and thus may 

 readily be confounded with the liber-cells in a cross sec- 

 tion. The proper vessels are distributed in two groups, 

 which, with the spiral vessels, form as it were the points 

 of a triangle inclosing the large vessel. 



Of the Structure of the particular Anatomical Systems 

 of the Vascular Bundle. 



The cells of that part which I denominate liber always 

 have a diagonal septum. In a young condition, they, 

 like all other thick- walled cells, are composed of delicate, 

 colourless membrane. When with increased age they 

 have become thicker, they afford clear evidence that the 

 membrane of the vegetable cell grows in thickness by the 

 deposition of layers. In transverse sections of the walls 

 of the liber-cells of all Palms, delicate concentric lines 

 may be seen, and that these lines form the boundaries 

 of the different layers composing the cell-membrane, is 

 manifest from the fact that sometimes, when the section 

 has been made with a razor which is not very sharp, these 

 layers separate from each other, and the slice of cell- 

 membrane appears in the form of distinct concentric 

 rings. Frequently the colour of these cells is not uniform 

 throughout the whole thickness of the membrane, and 



