PTERIDOPHYTA. 



523 



they decayed they left scars on the bark (figs. 1392 and 1393) 

 corresponding to the leaf-scars on the stems. The nature of the 

 fruit is still unknown, but it is probable that it more or less closely 

 resembled that of the Lepidodendroids. Sir J. W. Dawson has, 

 however, suggested that some of the Sigillarians may have had 



Fig. 1392. — Part of root of a Sigillarian or Lepidoden- 

 droid Tree (Stigmariaficoid.es) ; from the Carboniferous. 

 One-quarter natural size. 



Fig. 1393. — Bark of a Sigillarian 

 or Lepidodendroid root ; from the 

 Carboniferous. (After Dawson.) 



fruit of the type of Trigonocarpus (fig. 1400), and that such forms 

 consequently exhibit a connecting link between the Pteridophytes 

 and the Gymnospermous Phanerogams. 



The genus may be divided into several groups, which may eventually 

 have to be raised to generic rank. The Clathrarian group (in which Mr 

 Kidston includes some species of Ulodendro?i) has a thin bark, with the 

 leaf-scars not in distinct rows, but having a spiral appearance ; type, S. 

 discophora, of Europe and the United States. In the Liodermarian 

 group the ribs on the bark are obsolete, and the leaf-scars in distinct 

 rows ; type, S. sydnenszs, of Australia. In the third, or Rhytidolepidian 

 group, in which the Favularian group may be included, the ribs are 

 narrow (fig. 1391) and often striate, and the leaf-scars large and hexa- 

 gonal, or shield-shaped ; type, ^. tessellata (fig. 1389, B). Finally, the 

 typical group is characterised by the broad ribs to the bark, of which 

 the width usually exceeds that of the oval or elliptical leaf-scars ; types, 

 S. reniformis and S. Browni (fig. 1389, a). 



