454 



COENOPTERIDEAE 



[CH. 



phaliensis. The fossil described by Williamson as R. irregularis 

 or inaequalis^ are the secondary branches of A. bibractensis. 



Ankyropteris bibractensis, var. westphaliensis. Figs. 312, C; 313. 



The rachis stele of this species, which is represented by 

 portions of fronds only, has the form of a double anchor 

 (fig. 313); the antennae are continued at the outer edge of 

 their distal ends into a narrow band (" filament " of P. Bertrand) 

 (fig. 312, C, and 313, a) composed of smaller tracheae and 

 separated from the xylem of the antennae by a strip of thin- 

 walled tissue (phloem ?). A group of protoxylem occurs at the 



Fia. 313. Ankyropteris bibractensis: s, stigmarian rootlet; u., narrow loop of 

 xylem. (Cambridge Botany School ; x 6). 



junction of the filament and antennae. The whole of the xylem 

 is surrounded by phloem. 



The section reproduced in fig. 313 shows the characteristic 

 form of the petiolar vascular axis, consisting of a horizontal 

 band of metaxylem with groups of much smaller tracheae on 

 both the upper and lower margins. At the junction between 

 the antennae, curved like the flukes of an anchor, and the 

 horizontal band of xylem, the latter is only one trachea in 

 breadth. The narrow loops of smaller xylem elements are 

 1 Williamson (89) A. PI. viii. fig. 28. 



