COMPOSITION OF FIBRO-VASCULAR BUNDLES OF PLANTS. 397 



Falkenbergi considers^ with reference to Monocotyledons, 

 that by the history of their development, by the fact that all 

 intermediate forms are to be found between the ordinary 

 parenchymatous cell of the ground tissue and the prosenchy- 

 matous bast cell, it is clearly shown that the bast cells are 

 to be referred to the ground tissue, and he also agrees that 

 these cells are arranged in accordance with the laws of 

 mechanics. 



It will be interesting, in conclusion, to see how these views 

 affect our conceptions of the ground tissue and of the fibro- 

 vascular bundle. Before their publication Russow^ had 

 formed, from morphological considerations, much the same 

 conclusions as to the limits between the ground and vascular 

 tissues as Schwendener formed from physiological. Some of 

 his conclusions were criticised by Vochting,^ and were 

 regarded by him as obliterating all distinction between the 

 tissues in question. Russow,''^ however, points out that the 

 formation of the bast, in Monocotyledons, for example, and 

 more especially of that portion of it which is closely applied 

 to the bundles, must necessarily take place simultaneously 

 with that of the vascular elements themselves, in order to 

 afford protection and support to the young and tender tissues ; 

 and he argues that Vochting is incorrect in regarding the 

 bast cells thus formed as belonging to the vascular bundles, 

 and that this simultaneous origin from apparently the same 

 primitive tissue is insufficient evidence of morphological 

 equivalency. 



As to the fibro-vascular bundles themselves, we can regard 

 only the vessels of the phloem and of the xylem, together 

 with the parenchymatous cells which accompany them 

 (Geleitzellen), as being their essential morphological ele- 

 ments; and herein we follow the view of Schwendener — a 

 view which is also accepted by Falkenberg.^ 



When prosenchymatous cells occur in a bundle we must 

 regard them as elements of the bundle, but only as compara- 

 tively accidental elements, since their presence there is in 

 accordance, not with the morjihological principles which 

 regulate the arrangement of the parenchymatous cells in 

 connection with the vessels, but with principles of a purely 

 mechanical sort.^ 



1 Loc. cit., 1876, p. 138 and 158. 

 - 'Vergl. Untersuch.' 

 ' Loc. cit., p. 475. 

 •* ' Betrachtungeu,' p. ]4. 

 * Loc. cit., p. 155. 



"" Schwendener, loc. cit., p. 2. In his work these mechanical laws are 

 developed at length. 



