PTERIDOPHYTA— EQUISETIN^ 



151 



A transverse section of the rhizome, taken a little way 

 from the growing point, shows its exterior divided into ridges 

 and furrows. Opposite to each fiuTOW there is, a little 



way from the surface, 

 Fig. 908. Fig. 909. a large lysigenous 



intercellular cavity. 

 These together are 

 known as vallecular 

 cavities. They', are 

 interrupted at the 

 nodes, where a sheet 

 of parenchymatous 

 tissue stretches across 

 them. 



Fig. 910. 



Fi(/. 908. Fertile stem of Equisetum beariug a 



flower or cluster of sporophylls. Fig. 909. 



Sterile shoot of Equisetum. 



Fig. 910. Growing point of 

 shoot of Equisetum arvense. 

 X 250. a. Apical cell. 

 b, c. Successive segments 

 cut off from it. 



A little internal to 

 these cavities are the 

 several steles, the plant 

 being schizostelic. 



These are arranged 

 differently in different 

 species, and we may 

 distinguish three va- 

 rieties. In E. litorale 

 {fig. 911, a), the steles 

 are all separate, each 

 is clothed with peri- 



