no Mr. Thomas Hick on 



separated by a layer of cambium, and secondary medullary rays 

 are present. The vascular elements of the xylem are of the same 

 character as those of the central cylinder. 



3. Outside the zone formed by the secondary vascular bundles- 

 is the cortex, which is differentiated into distinct layers. Nearest 

 the phloem of the bundles it consists of a thin walled parenchyma 

 composed of cells of unequal size and irregular shape, among 

 which are numerous elements which Williamson describes as 

 elongated canals or cells containing a black substance. This- 

 substance is either in the form of a solid rod, or a hollow cylinder, 

 and the elements in which it is found give the cortex a character 

 which is remarkably distinctive. 



4. At the outer periphery of the cortex are two somewhat 

 irregular rows of cells, which are very clearly distinguishable from 

 the tissue within. Both these Williamson appears to regard as. 

 forming a distinct epidermal layer. 



The second series of Williamson's specimens have no 

 secondary vascular bundles. In them he describes the 

 following structures : — 



1. A central cylinder, pentagonal or hexagonal in outline, 

 composed like that of the preceding specimens, of vascular 

 elements intermingled with thin-walled cells. The vascular 

 elements are again pitted, and those at the periphery are again 

 smaller in diameter than those nearer the centre. 



2. A cortex of thin-walled, irregularly-shaped cells, interspersed 

 among which the elements with black contents are again met 

 with. 



3. A so-called epidermal layer, two cells in thickness, having 

 the same characters as that of the first series of specimens. 



The specimens of the third series are small in compari- 

 son with the others, and, as described by Williamson, have 

 a peripheral layer, two cells thick, and a cortex, which have 

 the same characters as those of the other series. The cen- 

 tral cylinder strongly resembles that of a rootlet, having 

 three, four, or more xylem strands arranged as in recent 

 rootlets. As to the nature of this group of specimens, 



