308 



CALAMITES. 



[CH. 



strands. It has already been pointed out that the xylem of 

 Equisetum increases in breadth at the nodes (p. 251, fig. 55, 4): 



Fig. 72. A. External xylem elements and eamblum, c, "with imperfect 

 phloem. X 100. 



B. Carinal canal containing protoxylem, px. x 65. 



C. Eadial longitudinal section through nodal xylem, px. x 35. 



D. Phloem elements; s, sieve-tubes; p, p, parenchymatous cells. 

 {A — C. After Williamson and Scott. -D. After Eenault.) 



the same is true of Calamites. In fig. 72, C, we have part of 

 a radial section of a Calamite twig in which the broad mass 

 of short nodal tracheids is clearly shown ; this nodal wood 

 forms a prominent projection towards the pith. In the lower 

 part of the section the remains of some spiral protoxylem 

 tracheids are seen in a carinal canal. 



The tracheids of the nodal wood are often reticularly pitted, 

 and so differ in appearance from the ordinary scalariform 

 elements. 



It is rare to find the phloem clearly preserved, but in 

 specimens where it has been possible to examine this portion of 

 the vascular bundles, it is found to consist of elongated 



