CORDAITALES 



173 



The leaf. — Taking the group as a whole, the leaves are in striking 

 contrast with those of the Cycadophytes. They are much smaller, 

 even the largest seldom exceeding a meter in length and 20 cm. in 

 width; while the smallest are needle-like and only a couple of centi- 



FiG. 183. — Cordaites {Araucarioxylon) brandlingii: A, longitudinal radial section of 

 stem, showing discoid pith (/»), and wood (.v); X7. B, longitudinal radial section from 

 the pith to the beginning of secondary wood; p, pith; px, first protoxylem; sp, later 

 spiral and sc, scalariform tracheids of primary wood; ht, pitted tracheids of secondary 

 wood; Xqs. — After Scott.s33 



meters in length. They are leathery, with a highly xerophytic struc- 

 ture. The margins are entire, and the venation dichotomous, with 

 so little forking of the veins beyond the base of the leaf that bota- 

 nists regarded them as parallel-veined leaves, and promptly made 

 the monocots older than the dicots by the sure evidence of geological 



