CYCADOFILICALES 



IS 



The leaf. — Of all the Gymnosperm leaves which caused the Car- 

 boniferous to be called the "Age of Ferns" none are better known than 

 those which belonged to Lyginopteris. Before the connection be- 

 tween leaf and stem was discovered the leaf of Lyginopteris oldhamia 

 was described as Sphenopteris hoenighausi (fig. lo). As in many 

 Cycadofilicales, the rachis forked, and the forks bore strong pinnae, 

 which were again pinnate. Twice- and thrice-pinnate leaves of both 



Fig. 9. — Lyginopteris oldhamia: x^, secondary wood; cb, cambium; ph, primary phlo- 

 em; p/i-, secondary phloem; ss, secretory sac; pd, periderm; X52. — After Williamson 

 and Scott. 



Cycadofilicales and ferns, some of them strongly dimorphic, were 

 common in the Carboniferous (fig. 11). 



The histological structure is not very different from that of living 

 plants with leaves of this habit. The epidermis is cutinized on the 

 adaxial surface, there is a palisade and a spongy parenchyma, and 

 the stomata are on the under side. The leaves have strong spines 

 which are rounded and glandular at the tip. Similar spines on the 

 stem and leaf stalk suggested to Williamson that Rachiopteris as- 

 persa, Lyginodendron oldhamium, and Sphenopteris hoenighausi were 

 the leafstalk, stem, and leaf of the same plant, which we now call 

 Lyginopteris oldhamia. 



The root. — Roots are abundant and splendidly preserved, so that 

 the name, Kaloxylon, was well chosen. Some of them, especially 



