94 



MORPHOLOGY OF GYMNOSPERMS 



(leaf traces). The contrast with stems of Ginkgoales and Coniferales 

 is striking, these groups having relatively small pith, very thick 



Fig. 71. — Dioon spinulosiim: on the Hacienda de Joliet near Tierra Blanca 

 (Mexico), March 1908; the tallest plant is about 10 m. in height. — After Chamber- 

 lain (64). 



v^ascular cylinders, and a comparatively thin cortex. Systems of 

 mucilage canals occur in the cortex and in the pith, connecting with 



