GNETALES— EPHEDRA 



367 



angiosperms. There is no other gen- 

 eral breaking down of the oblique 

 walls to form continuous vessels. 



Most of the wood consists of tra- 

 cheids with bordered pits, usually 

 uniseriate, and more abundant on 

 the radial face, but there is also 

 abundant tangential pitting (fig. 



348). 



Medullary rays are very long and 

 very wide (fig. 348). Only about 

 one-third of the two long rays is 

 shown in the figure, with the top of 

 another at the lower left. The cells 

 of the rays are of various shapes 

 and sizes: isodiametric, elongated, 

 and curved. The walls are thick, 

 lignified, and pitted, but the pits are 

 small and simple. 



Rays in young plants are uni- 

 seriate, but, later, they become 

 multiseriate by longitudinal divi- 

 sions in the uniseriate ray, by the 

 incorporation of adjoining cells, or 

 by the fusion of uniseriate rays. 

 When there is a fusion of uniseri- 

 ate rays, separated by a few tra- 

 cheids, the tracheids are incorpo- 

 rated in the large resulting ray. 

 Such rays have no relation to leaf 

 traces. 



With practically all of the cells 

 thick walled and lignified, it is 

 natural that the wood should be 

 very hard. In young stems the 

 rigidity is also increased by lignifi- 

 cation of the pith just above the 



Fig. 348. — Ephedra trifurca: longi- 

 tudinal tangential section, showing the 

 ends of two large medullary rays, and 

 a tip of a ray at the lower left. Many 

 cells of the ray are pitted, and in the 

 long tracheids there is both radial and 

 tangential pitting; X170. 



