88 THE PALM-STEM : 



bundles run down to the base of the stem in the form of 

 a close fibrous network, and that in consequence of the 

 continued deposition of new fibrous layers, the stem ex- 

 hibits an uninterrupted growth in thickness, while in the 

 Palms the lower fibrous extremities of the vascular 

 bundles, as a general rule, remain simple, and do not run 

 downwards to the base of the stem. The case observed 

 by me in Co cos, of the solution of the vascular bundles 

 into a number of slender fibres (p. 9) is to be regarded 

 as an approximation, in the Palms, to the structure of this 

 fibrous reticulation. These differences occurring between 

 the stem of Yucca and that of the Palms are undoubtedly 

 not of sufficient importance to allow of our supposing an 

 essential difference to exist in the mode of development 

 of the vascular bundles. Since, then, in every Monoco- 

 tyledonous stem vascular bundles appear, in consequence 

 of the development of a branch, which, without the for- 

 mation of that branch, would not have originated, since 

 these vascular bundles form a greater mass, and spread 

 so much more widely over the stem from the base of the 

 branch, the older this latter becomes, since in Yucca the 

 course of the vascular bundles exhibits such mechanical 

 conditions in the vicinity of a wound on the stem, as 

 must result from a downward growth of the vascular 

 bundles on the stem, it is quite justifiable for me to de- 

 clare that Mirbel's view, that the vascular bundles of the 

 Palms grow from below upwards, is an opinion opposed 

 to the phenomena of the growth of the Monocotyledons ; 

 and to presume, on the contrary, that the lower portion 

 of these bundles is developed in the direction from above 

 downwards. 



Meneghini came to the same result through a series of 

 deductions altogether different from mine. He had already- 

 stated, in his first paper on the structure of Monocotyledons 

 (Richerche sulla Struttura del Caule nelle Piante Monoco- 

 tiledoni, 1836, p. 77), that the formation of vascular 

 bundles was caused by definite currents of nutrient sap, 

 without, however, carrying out this view more minutely. 



