APPENDIX. 81 



and is blended with the upturned margins of the pinnae, 

 whence the slits between the latter are only visible at the 

 under side of the leaf. The leaf, therefore, originates as 

 a continuous mass, and the pinnae owe their origin to an 

 actual division of the leaf : the division, however, does 

 not advance from the margin of the leaf toward the mid- 

 rib, but relates only to the surface, not affecting the 

 border, nor, in Phcenicc, the upper layer of the tissue of 

 the leaf. This permanently undivided mass of cells is 

 distinguished from a true pubescence, to which it bears 

 much resemblance, by its origin, since it is not a growth 

 from the surface of the organ, but forms an actual part 

 of the tissue of the leaf, as well as by the circumstance 

 that in some of the Palms, for example in Phoenix (but 

 not in Cocos), vascular bundles run into it. 



Return we from this digression, to Mirbel's description 

 of the bud. He states that there run through the tissue 

 of the bud a countless number of transparent, very deli- 

 cate fibres, which converge from the whole internal 

 periphery of the stem toward the central portion of the 

 phyllophore, where their upper extremities approach the 

 young leaflets, sooner or later to enter into direct con- 

 nexion with them. In a few instances he has hit upon 

 these fibres at the moment when they were running into 

 the weakly -indicated rudiments of the leaves. Those 

 physiologists who believe that the fibres run down from 

 the leaves had certainly never an opportunity of seeing 

 the terminal bud of a vigorous Date-palm, or they would 

 have left nothing for him to do. A glance is sufficient 

 to convince that the upper ends of these fibres are very 

 young compared with the lower, that they consequently 

 grow from below upwards. If they sprang from the 

 leaves, they must be old and hardened at their point of 

 origin, long before they reached the base of the stem. 



This proposition contains the nucleus of Mirbel's doc- 

 trine of the structure of the Monocotyledons. The remark 

 that earlier labourers at the anatomy of Palms had no 

 terminal bud of a vigorous stem to examine, is unfortu- 



6 



