RELATIONS OF CALAMODENDRON TO CALAMITES. 261 



of the cast, fig. i, a, are due. In like manner, the origin 

 of the longitudinal grooves and ridges, b, running verti- 

 cally along each internode is illustrated by fig. 2, which 

 represents a fragment, including a node and parts of 

 two internodes, of a decorticated Calamite. Here a is 

 the fistular medullary cavity ; b a thin film of medullary 

 parenchyma which surrounds the fistular cavity ; c c is 

 a ring of vascular wedges ; the sharp apex of each wedge 

 projects inwards, encroaching upon the medullary zone, 

 at which latter point a narrow vertical canal *, d, is present. 

 All the wedges of each internode extend vertically in 

 parallel lines, e', as do the homologous vascular bands of 

 living Equisetums, through the entire length of the inter- 

 node ; but those of each internode alternate at each node, 

 /, with the corresponding wedges of the next internode 

 above and below. Each of these vascular wedges origin- 

 ated in a few vessels in contact with the longitudinal 

 canal, d; but as each wedge grew exogenously, its peri- 

 pheral, tangential diameter increased. 



Viewed in transverse section, as in the upper part of 

 fig. 2, we see that these wedges were separated widely 

 from one another in their youngest state by a broad radi- 

 ating band, g, of the fundamental parenchyma, connect- 

 ing the medulla with the cortex, exactly as the proto- 

 xylems of any young, vascular, exogenous growths are 

 separated from one another. In 1870 I applied to these 

 cellular bands in the young Calamite, the name of primary 

 medullary rays f, to distinguish them from those which 

 instead of commencing in the bark commence in the 

 wedges, and to which latter I applied the term secondary 



* In my yarious writings I have designatod this the internodal oanal, 

 regarding it as the homologue of the canals tljat accompany the vascular 

 bundles in the recent Equisetums. 



t " On the Oi-ganization of the Fossil Plants of the Coal-Measures. — 

 Tart 1.," Phil. Trails. (1871), p. 479. 



