32 THE PALM-STEM. 



hence injured places upon the stem, over which no new 

 layers are deposited, are gradually converted into depres- 

 sions. On account of this continuous deposition of new 

 layers, the assertion made by Dupetit-Thouars (premier 

 Essai) and received into all botanical works, that the stem 

 of Draccena does not increase in thickness so long as it 

 remains without branches, is incorrect, and it is easy to 

 convince one's self of this by the comparison of young 

 and old specimens ; thus, I found that the stem of a 

 Dracaena Draco, two feet high, was only about one inch 

 thick, while trunks twenty to thirty feet high had attained 

 a thickness of from four to six feet, although devoid of 

 branches. 



Aloe has exactly the same structure as Draccena, only 

 the outer firm layer is very thin in proportion to the 

 soft centre. Thus, in a stem of Aloe glauca two inches 

 thick, it was only two lines ; while in a stem of Dractena 

 Draco, two inches thick, it had already reached a thick- 

 ness of six lines. The vascular bundles of Aloe resemble 

 those of the Palms still less, for the vessels are scattered 

 irregularly in the woody portion ; however, the anterior 

 always have the form of reticulated, and the posterior of 

 spiral vessels. 



Comparing the stem of other Monocotyledons with 

 that of the Palms, in reference to the course and organi- 

 zation of the vascular bundles, we find in all (excepting 

 the very lowest forms), if not so great a similarity as in 

 Drac&na, yet a great analogy. It is, namely, common to 

 all Monocotyledons for the small evascular bundles to 

 lie at the periphery of the stem, while those lying further 

 in contain a bundle of proper vessels, to which succeed 

 bundles possessing large and small vessels, while the fully 

 developed lie toward the centre of the stem. 



These bundles exhibit more or less deviation from those of the Palms, in 

 reference to their intimate structure ; but that they are all formed after one 

 and the same type is unmistakeable. In general, the liber-layer is developed 

 in a much less degree than in the Palms ; for in many only the outer small 

 bundles exhibit an investment of thick-walled prosenchymatous cells, while 



