XXIX] LYGINOPTERIDEAE 49 



B show the gradual divergence of the two meristeles of a petiole 

 as they approach the level where it divides into two equal branches, 

 a characteristic feature of Sphenopteris Hoeninghausi and allied 

 fronds. At a lower level than that represented in fig. 406 the 

 vascular strand of the petiole would have the form of a W as 

 figured by Williamson in one of his earlier memoirs 1 . The phloem 

 with scattered secretory sacs and the adjacent tissue of the leaf- 

 stalk are occasionally preserved in wonderful perfection 2 . No 

 endodermis has been recognised. Sclerous nests are scattered in 

 the ground-tissue as are also secretory sacs (figs. 404, E ; 405, A). 

 A small root r has penetrated the parenchyma of the rachis shown 

 in fig. 405, A. 



FIG. 406. Lyginopteris oldhamia. Transverse section illustrating branching 

 of petiole, x 5. (From a drawing supplied by Prof. Oliver.) 



Sphenopteris Hoeninghausi Brongn, 3 , founded on material from 

 English Coal Measures, was regarded by Williamson as the foliage 

 of Lyginopteris chiefly on the ground of the occurrence of emer- 

 gences on the axes (figs. 404, A, B) and laminae of the impressions 

 like those on the petrified stems, and this comparison received 

 support from the resemblance of the fragments of pinnules asso- 

 ciated with Lyginopteris and its petioles in the calcareous nodules 



1 Williamson (74) PI. LI. fig. 1. 



2 Scott (09) B. fig. 139, p. 375. 



3 Brongniart (28) A. p. 199, PI. LIT. For synonymy, see Kidston (11) p. 42. 



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