90 THE PALM-STEM : 



the vascular bundles must, in respect to the organic for- 

 mation, be regarded as descending from the nascent leaf 

 in the centre of the bud. 



Returning to Mirbel's exposition, the manner in which 

 the vascular bundles terminate below in Phwnix is not 

 minutely described by him. Neither have I, as already 

 observed, been fortunate enough to make out this point 

 with certainty. It is indeed found, as I stated in my 

 description of the Palm-stem, that a part of the vascular 

 bundles becomes blended with others below, or as phy- 

 totomists who ascribe an ascending course to them ex- 

 press it, are branches from other vascular bundles entering 

 into leaves situated lower down ; but this condition can 

 only be demonstrated in a very small portion of them, 

 and, in particular, not in the capillary fibres, in which 

 the vascular bundles terminate in the outer layers of the 

 stem. It is probable, therefore, that the majority of the 

 vascular bundles terminate blindly in the cellular tissue 

 beneath the rind. This assumption may appear to create 

 a difficulty in regard to the explanation of the manner in 

 which the sap ascends, but we find exactly the same 

 condition in the vascular bundles of the corona of many 

 Dicotyledons for example, in Laurus nobilis, Quercus, 

 Rosa; where the vascular bundles running into one leaf run 

 down the stem without entering into any connexion with 

 those of another leaf, and become gradually attenuated 

 under the form of thin fibres, which cannot be traced 

 farther down. In these plants, the ascending sap, when 

 it flows through one vascular bundle, must, to reach a 

 second, emerge laterally into the cellular tissue, and from 

 this flow into the neighbouring vascular bundles. The 

 condition, however, as I have already several times re- 

 marked, does not occur in all the arborescent Monocoty- 

 ledons, since in Dractena, Yucca, Xanthorrhcea, the lower 

 extremities of the vascular bundles grow together at their 

 sides, and in this way form a connected fibrous reticula- 

 tion over the whole stem. 



Mirbel distinguishes different kinds of vascular bundles 



