The Primary Structure of the Stem of Calamites. 161 



little more than the carinal canal, formed by the breaking 

 down of the initial strand of vessels. A striking and 

 remarkable feature of some of these canals is the presence, 

 at the margin, of projecting elements, which I have no 

 hesitation in interpreting as the remnants of the vessels, v. 

 The presence of these elements gives the canals an 

 appearance which is perfectly identical with that of the 

 homologous canals of Equisetum, but the lateral xylem 

 elements found in the latter plant are not distinguishable. 



External to each canal is a mass of small elements,/, 

 which, from their position and their distinct character when 

 compared with the ground tissue on either hand and 

 between the canals, must be regarded as the phloem of the 

 primary bundles. It is true that some of the histological 

 characters of phloem cannot be recognised in these groups 

 of elements, but this is most probably due to the fact that 

 in the process of fossilisation, their contents have all 

 disappeared. If, however, they be compared with the 

 phloem of Equisetum after the protoplasm, &c, has been 

 removed, it will be found that they are in close agreement 

 therewith not only in position, but in the size and general 

 arrangement of the constituent elements. If a pericycle 

 ever existed outside this phloem, it is no longer recognisable. 



Still moving outward, we next come to a sharply 

 defined line, s, which is traceable nearly all round the stem, 

 just outside the ring of primary vascular bundles. The line 

 is slightly undulated, the parts opposite the bundles being 

 convex, and those opposite the medullary rays concave, 

 outwardly. I regard it as marking the boundary between 

 the stele, or vascular-bundle cylinder, and the cortex. In 

 most of my preparations, it is apparently a simple but thick 

 black " line," but in the one under description, and one or 

 two others, there are vague indications of a single layer of 

 narrow cells in place of the " line " at some points. If this 

 could be proved to be the normal structure, few would 



