l82 
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. 4 i8). This char- 
acter distinguishes Cyca- 
dofilicales from ferns, but 
it would not serve to sepa- 
rate them from P terid - 
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 
been found in connection 
FIG. 418. Photograph of cross section of vascular 
cylinder (ectophloic siphonostele) of Lyginodendron, 
showing the secondary wood characteristic of Cycado- 
filicales. Photograph by BOODLE. 
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; 430, two seeds of L. Sindairi 
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 
