158 STUDIES IN FOSSIL BOTANY 



of Williamson, and by the late M. Hovelacque * in L. 

 selaginoides. It has since been demonstrated in several 

 other species, and was probably common to the whole 

 family. 



In all the species in which the ligule has been 

 found, it presents much the same features. Its position 

 is always on the upper surface of the cushion, immedi- 

 ately above the leaf-scar. 



The ligule is seated at the base of a deep flask- 

 shaped cavity, and is very rarely found projecting 

 beyond it (see Figs. 62, B, and 63, Ig). The ligule 

 was, of course, a delicate organ, and is often imper- 

 fectly preserved ; often the ligular cavity is shown, 

 when the ligule itself has perished altogether. In some 

 cases, however, the cellular structure of the ligule is 

 perfectly shown, and is found to agree, on the whole, 

 with that in recent Ligulatae. The deep ligular cavity 

 is very characteristic of Lepidodendreae, but is not 

 without parallel among recent plants, for Professor 

 Harvey Gibson has shown that in Selaginella oregana 

 and rupestris " the free margin of the ligule scarcely 

 appears above the edge of the very deep pit in the leaf 

 in which it is seated." 2 



The base of the ligular cavity lies just above the 

 vascular bundle, and is in many cases, if not in all, 

 surrounded by a sheath of short tracheides, forming a 

 connection with the wood of the leaf- trace bundle, 

 just as in Iso'etes and in some Selaginellae among recent 

 plants. The cavity slopes from its base, upwards and 



1 " Recherches sur le Lepidodendron selaginoides," Mem. de la Soc. 

 Linnienne de Normandie, Caen, 1892. 



2 "Anatomy of the Genus Selaginella," Part ii. The Ligule, Annals 

 of Botany, vol. a. p. 83, Plate viii. Fig. 19, 1896. 



