APPENDIX. 71 



vascular bundle of the Dicotyledons as a growth belonging 

 to the vascular bundle itself, while I had derived it from 

 the interposition of the lower ends of younger vascular 

 bundles, running to leaves situated higher up, between 

 the liber and wood of the old bundles ; a theory against 

 which Unger, also, has declared himself with convincing 

 reasons (Ueber den Bau und das Wachsthum des Dico- 

 tylenstammes) . Perhaps it may not be superfluous to 

 remark, that this distinction only refers to part of the 

 vascular bundles of the Dicotyledons, since the part en- 

 tering the leaf and traversing it is likewise limited in its 

 increase of thickness. 



I now turn to Mirbel's excellent essay on the Structure 

 of the Date-palm (Comptes rendus de 1' Academic des 

 Sciences, 12 June, 1843). In 1839 the author went to 

 Algiers, in order to have an opportunity of examining a 

 full-grown Date-palm in a fresh condition ; and as the 

 result of four years' labour, directed especially to the in- 

 vestigation of the terminal bud of this Palm, he laid 

 before the Paris Academy a theory of the structure and 

 growth of the Monocotyledons, which is opposed to my 

 statement in several points. 



With reference to the connexion of the roots with the 

 stem, Mirbel agrees on the whole with my views, but 

 assumes a more intimate connexion of the vascular bundles 

 of the roots with those of the stems, than I met with in 

 my researches. According to his statement, the fibres 

 which come from the middle and neighbouring parts of 

 the root, penetrate into the interior of the stem, between 

 the vascular bundles of the latter, and lose themselves 

 among them, in such a way that their extremities cannot 

 be accurately made out, while fibres derived from the 

 circumference of the expansion formed by the root in the 

 stem, are distributed upwards and downwards, in the 

 superficial layers. In reference to the latter, Mirbel thinks 

 that they probably furnish contributions to the suckers 

 which break forth abundantly from the base of the stem 

 in the Date-palm and Chamcerops; of the former, Mirbel 



