314 



CALAMITES. 



[CH. 



long and narrow parenchymatous cells ; as the section is tan- 

 gential the characteristic scalariform character of the tracheids 

 is not shown, the ladder-like bordered pits being confined to 

 the radial walls of the tracheal elements. The much greater 

 length than breadth of the cells which form the rays associated 

 with the xylem tracheids, is a characteristic feature in Calamitean 

 stems. The breadth of the principal ray, m, shows that the 

 section has passed through the wood a short distance from the 

 pith ; in a tangential section cut further into the wood the 

 breadth of the principal rays would be considerably reduced. 

 The large medullary-ray tissue consists of square-walled 

 parenchymatous cells. The more highly magnified section, in 



Fig. 76. Longitudinal tangential section of the same Calamite as that of figs. 

 74 and 75, showing a leaf-trace and curved tracheids at a node. 

 From a section in the Binney Collection, x 100. 



fig. 76, shows a central group of parenchyma containing a 

 few transversely cut tracheids, but the two kinds of elements 

 are not clearly differentiated in the figure ; this group of cells is 



