92 STUDIES IN FOSSIL BOTANY 



remarkable characteristics. It consists of radial series 

 of tracheae, of large size, with numerous bordered pits, 

 chiefly on the radial cell-walls (Fig. 39). Between these 

 tracheae, which, as seen in transverse section, appear 

 square with truncated angles, we find little groups of 



Fig. 38. — Sphenophyllum plurifoliatum. Transverse section of older stem, showing 

 triangular primary wood, broad zone of secondary wood, remains of phloem, and 

 thick periderm ; primary cortex cast off. X 18. From a photograph. Phil. Trans., 

 W. and S. Will. Coll. 899. 



thin-walled cells, fitting into the spaces at the corners 

 (see Fig. 36, D). These represent vertical strands of 

 parenchyma, which are not isolated, but are connected 

 with one another, in the radial direction, by horizontal 

 cells or strands of cells, which are usually quite short, 

 not forming continuous medullary rays (Figs. 36, D, and 



