APPENDIX, 91 



in the stem of the Date-palm : 1st, those which occur in 

 the interior of the stem, and form the principal mass of 

 its wood ; 2d, capillary fibres, which lie in great numbers 

 in the peripherical region of the stem and the petiole, 

 do not occur in the interior of the stem, and are thirty- 

 six times smaller in diameter than the first. These thinner 

 fibres contain no vessels, but are composed merely of 

 elongated, thick-walled cells. In my description of the 

 Palm-stem, I have likewise directed attention to these 

 differences, and mentioned that the second class of fibres 

 are the inferior extremities of bundles, which, without 

 previously entering into the interior of the stem, run in 

 the outer layers of the stem, and are here mostly con- 

 verted into true vascular bundles, linger was the first 

 to remark that these fibres are of later origin than the 

 vascular bundles lying in the interior of the stem ; but 

 Meneghini called especial attention to the circumstance, 

 that, as a general rule, the different vascular bundles of 

 the same leaf do not all penetrate to the same depth in 

 the stem, and that this difference depends on the circum- 

 stance that the leaf, during its development, passes out from 

 the centre of the axis to the periphery, and each vascular 

 bundle only reaches that point in its internal curve, at which 

 the leaf was actually situated at the moment when the 

 organization of the vascular bundle commenced (Intorno 

 alia Struttura del Tronco delle Monocotiledoni, p. 12). 



Mirbel brings a portion of the vascular bundles promi- 

 nently forward under the name of precursors (precurseurs). 

 He applies this name to them because they are the first 

 which become connected with the leaves. According to 

 him, their number equals that of the leaves in each step of 

 the leaf-spiral (de chaque pas d'helice), and they appear at 

 intervals, which are measured by the length of the inter- 

 nodes. They lie in a bundle in the centre of the stem ; 

 each of them proceeds singly out of this central bundle, 

 and passes obliquely upward into a leaf. On its way, a 

 number of other vascular bundles attach themselves to 

 it. At the point where the precursor leaves the vertical 



