The Primary Structure of the Stem of Catamites. 167 



complete and in a much finer state of preservation than 

 any other section I have yet come across. In it will be 

 seen the pith, a, surrounded by the carinal canals, d, seven- 

 teen in number, arranged as in the younger specimens. 

 But outside each carinal canal is a wedge-shaped mass of 

 secondary xylem, x, and between these masses are the 

 somewhat broad medullary rays, r. It will be noticed that, 

 as has been pointed out by several observers, 1 the first 

 formed elements of the secondary xylem stand near or 

 abut upon the carinal canals, and the rest are developed 

 centrifugally in radiating rows. Hence, as the young stems 

 described in this paper show phloem strands in immediate 

 proximity to the canals, 2 it seems a warrantable inference 

 that the secondary thickening begins in the position usual 

 for open collateral bundles, i.e., between the phloem and 

 the xylem. 



As the development of the secondary xylem would 

 necessitate the displacement of the phloem and the ' line ' 

 of demarcation between the stele and the cortex, one 

 naturally looks for traces of these in the older stems ; but 

 so far I have not been able to detect them. It is otherwise, 

 however, with the cortical tissues. At i we have the inner 

 cortical zone of the older stem, and it needs little examina- 

 tion to see that it is identical with that of the primary stem. 

 (Fig. 1, z.) The arrangement and general appearance of the 

 elements are the same in both cases, and the same may be 

 said of their histological structure. The breadth in the older 

 stem, as in the younger, is yi^ inch, so that there has been 

 no growth in the radial direction. Obviously, however, 

 there must have been growth in the tangential direction, as 

 the layer still completely encircles the stem, though not 

 quite so uninterruptedly as in the earlier stage. 



1 See especially Binney loc. at., and Williamson, Philosophical Trans., 1871. 

 2 Ante, p. 



