APPENDIX. 73 



does not exist. This investigation is far more difficult at 

 the place of union of the root with the stem ; but in a 

 few Palms, particularly in a Cocos stem, in which the 

 cellular tissue had been destroyed by rotting, I examined, 

 at the point of entrance of several roots, the interlacement 

 which their vascular bundles formed with those of the 

 stem, and traced separately all the vascular bundles which 

 ran through these, without finding a transition of a root- 

 bundle into a stem-bundle ; I therefore think that I may 

 safely deny the occurrence of such a transition, at least in 

 these cases. At the same time I do not wish to question, 

 that in other cases part of the vascular bundles entering 

 the stem from the root become mingled with the bundles 

 of the former, and run on with them, as I have myself 

 stated this to be the case with the fibrous bundles, which, 

 in some Palms, lie with their lower extremities in the 

 rind of the root, and as Meneghini found in the isolated 

 fibres of the woody portion of the roots of Chamcerops ; 

 but I believe I may deny that this condition occurs always 

 and necessarily, and that a conclusion adverse to the in- 

 dependence of the vascular-bundle system of the Mono- 

 cotyledons is to be deduced from it. 



In regard to the structure of the stem, Mirbel directed 

 his attention chiefly to the settlement of the question, 

 whether the vascular bundles grow downwards from the 

 leaves into the stem, or are developed in the contrary 

 manner. He is in doubt whether, in my description of 

 the Palm-stem, where I have described the course of the 

 fibres downwards from the leaf, I merely intended to de- 

 note the mechanical conditions of their position, or the 

 direction in which they are formed. I scarcely think that 

 I could have expressed myself more distinctly on this 

 point, that I meant only the former. I was unwilling to 

 propound any definite opinion on the second question, 

 because, in the absence of sufficient material, I was unable 

 to solve it with certainty. 



Mirbel first investigates the question, whether the vas- 

 cular bundles run down from the leaves to the base of the 



