182 



MORPHOLOGY 



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

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



is a development of second- 

 wood 



ary 



n varyng 



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 



FIG. 418. Photograph of cross section of vascular Equisetales). 

 cylinder (ectophloic siphonostele) of Lyginodendron, Seeds. _ The seeds of 

 showing the secondary wood characteristic of Cycado- ~ , r , . , , 



filicales. - Photograph by BOODLE. Cycadofilicales have now 



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 



