328 



CALAMITES. 



[CH. 



French and German silicified specimens\ There is the same 

 large hollow pith surrounded by a ring of collateral bundles 

 with carinal canals, as in the two preceding subgenera. The 

 tracheids are scalariform and reticulate, and the secondary 

 medullary rays consist of rows of parenchymatous cells which 

 are longer than broad, as in Arthropitys and Arthrodendron. 



The most characteristic feature of Calamodendron is the 

 occurrence of several rows of radially disposed thick-walled 

 prosenchymatous elements (fig. 84, b) on either flank of each 



Fig, 84. Calamites [Calamodendron) intermedium, Ken. 

 Transverse section through two vascular bundles. 



a, a, xylem tracheids, h, h, bands of prosenchyma, c, medullary ray. (After 

 Kenault.) 



wedge-shaped group of xylem. Each principal ray is thus 

 nearly filled up by bands of fibrous cells on the sides of adjacent 

 xylem groups, but the centre of each principal ray is occupied 

 by a narrow band of parenchyma (fig. 84, c). The relative 

 breadth of the xylem and prosenchymatous bands has been 

 made use of by Renault as a specific character in Calamoden- 

 dron stems. Fig. 84 is copied from a drawing recently published 

 by this French author of a new species of Calamodendron, 

 C. intermedium^. In this case the bands of fibrous cells, b, 

 are slightly broader, as seen in a transverse section of the 



1 Vide Williamson (87-). In this paper Williamson compares the three 

 subgenera of Calamite stems. Renault and Zeiller (88), PI. lxxv. Renault 

 (93), Pis. Lviii. and lix. 



2 Renault (96), p. 125; (93), PI. lix. fig. 2. 



