182 



MORPHOLOGY 



ing Heterangium (protostele), Lyginodendron (ectophloic siphonostele), 

 and Medullosa (polystele). Among the Cycadofilicales, however, there 



is a development of second- 

 ary wood in varying 

 amount, but always dis- 

 tinct (fig. 418). This char- 

 acter distinguishes Cyca- 

 dofilicales from ferns, but 

 it would not serve to sepa- 

 rate them from pterido- 

 phytes, for secondary wood 

 was formed by many of the 

 older pteridophytes (as the 

 extinct Lycopodiales and 

 Equisetales). 



Seeds. The seeds of 

 Cycadofilicales have now 



FIG. 418. Photograph of cross section of vascular 

 cylinder (ectophloic siphonostele) of Lyginodendron, 

 showing the secondary wood characteristic of Cycado- 

 filicales. Photograph by BOODLE. 



been found in connection 

 with all the great frond genera of the Carboniferous. The leaves 

 or the pinnae which bear seeds usually differ in form from the sterile 



419 



FIGS. 419, 420. Seeds of Cycadofilicales: 419, seed of Lagenostoma Lomaxi (restored 

 by OLIVER), showing the investing glandular cupule; 420, two seeds of L. Sinclairi 

 terminating naked branches. After ARBER. 



leaves or pinnae, the seeds terminating naked branches and often 

 being invested by husklike cupules (figs. 419, 420, 421), as if the 



