LECT. VIII.] STRUCTURE OF LIGNEOUS ROOTS. 407 



part, when placed under the microscope, displays 

 nearly the same structure as the corresponding 

 part above ground. Thus in the bark we find the 

 cuticle with its horizontal vessels terminating in the 

 parenchyma; the cellular Integument consisting 

 of regular hexagonal cells ; and the liber display- 

 ing its reticular meshes. The cells, however, are 

 larger than those of the caulinar bark, and are 

 filled with a fawn-coloured instead of a green 

 fluid. The circle of alburnum and of wood differ 

 in nothing from those of the stem ; except that the 

 vessels, which are also cribriform, and the cells 

 of the divergent layers contain numerous trans- 

 parent granular bodies, which are likewise found 

 crowding the cells of the medullary sheath and 

 those of the pith. I have not been able to dis- 

 cover any spiral vessels in the medullary sheath of 

 the root-caudex, even in the youngest trees ; in 

 which particular, therefore, the root differs from the 

 stem. The pith, which is larger than that of the 

 stem, consists of hexagonal cells, turgid with fluid, 

 and so crowded with the granular bodies already 

 described, as to obscure their hexagonal structure, 

 which, however, can be distinctly observed in a 

 very thin section. 



Such is the root-caudex of the Horse Chesnut 

 in the second or third year of its growth; and it 

 may be taken as an example of the structure of this 



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