APPENDIX. 67 



sides, and that their intermediate portion is to be regarded 

 as their most essential part, since it is not merely that 

 first originating, but also, in all stages of metamor- 

 phosis of the vascular bundle, persists under the same 

 form of elongated cells, resembling milk-vessels. 



In reference to the blending of the vascular bundles 

 with each other, Unger distinguishes the proper blending 

 (coalifus), which consists in the actual fusion into one 

 vascular bundle, from the mere apposition (symphysis) , 

 in which the vascular bundles are attached together by a 

 dense parenchyma. According to Unger, true blending 

 does not occur in the Aloinece (with the exception of 

 Yucca gloriosa and Agave Americana), while in other 

 families, especially in the Scitaminese and Bromeliaceae, 

 it is frequent. 



Of the systems of vascular bundles of the buds and 

 roots of the Grasses, it is stated, that they are special to 

 these organs, and do not pass into them from the stem ; 

 this is particularly evident in the roots, but in the vascu- 

 lar bundles of the buds also, a mere anastomosis with 

 the vascular bundles of the stem occurs, and only indivi- 

 dual ones become mingled with those of the stem. 



With regard to the period at which the vascular 

 bundles running to a leaf originate, Unger found that the 

 slender fibres occurring in the Palms and Grasses, which 

 do not enter into the interior of the stem (at least, cer- 

 tainly not in the Grasses), are of later origin than the 

 stronger vascular bundles which run from the inner layers 

 of the stem into the leaves. 



Lestiboudois expresses an opinion very different from 

 that of his predecessors, in reference to the mutual blend- 

 ing of the vascular bundles, in his very^aluable treatise 

 on the Structure of the Stems of Plants (Etudes sur 1' Ana- 

 tomic et la Physiologic des Vegetaux, 1840), in which he 

 has wholly relinquished his earlier views of the structure 

 of the Monocotyledonous stem. 



The Palm-stems examined by Lestiboudois belonged 

 to species, the systematic names of which are unknown 



