LYGINODENDRON 377 



fairly coriaceous Fern-leaflet at the present day, and 

 indicates that the conditions to which the structure was 

 adapted could not have been fundamentally different 

 from those which prevail in our own epoch. 



A xerophytic structure is clearly exhibited in the 

 presence of a hypoderma, the considerable thickness of 

 the leaflets, and their conchoid, incurved form. Such 

 indications of xerophytic adaptation are exceedingly 



Fig. 140. — Lyginodeiidron oldhttmiuni. Vertical section of a leaflet, ejr, upper epi- 

 dermis ; Jiy, hypoderma ; /./., palisade-parenchyma ; sp., spongy parenchyma ; v.b., 

 vascular bundle ; e, spine. X about 70. From a photograph. Phil. Trans., W. and 

 S. Will. Coll. 1196. 



common among the plants of the Coal-measures, as 

 already noticed in the case of Sigillaria (p. 225, vol. i.). 

 The ends of the vascular bundles of the leaflets in 

 Lyginodendron are commonly dilated as regards the 

 xylem, a character which has also been observed in the 

 xerophytic leaves of the Mangrove plants of tropical 

 sea-shores. 



The proof that the Splienoptevis form of foliage just 

 described, which in structure, as well as in form and 

 venation, is essentially Fern-foliage, really belonged to 



