36 PTERIDOSPERMEAE [CH. 



subsequent paper Williamson 1 gave a fuller description of Binney's 

 species and spoke of it as ' one of the most common plants in the 

 calcareous nodules of the Lower Coal Measures' of Lancashire 

 and Yorkshire. He connected certain casts of arborescent 

 dimensions with Binney's type on the ground that the surface- 

 features of the casts are such as would be produced by partially 

 decorticated stems having a hypodermal reticulum of mechanical 

 tissue like that preserved in the small petrified specimen described 

 by Binney (fig. 402). Mr Carruthers called Williamson's attention 

 to a paper by Mr Gourlie 2 in which the generic name Lyginodendron 

 is instituted for stem-casts identical in surface-features with the 

 fossils figured by Williamson. In spite of the much larger dimen- 

 sions of the reticulum on the casts described by Gourlie as compared 

 with that in the outer cortex of Binney's stem, Williamson con- 

 cluded that Lyginodendron is 'undoubtedly an inorganic cast of 

 the prosenchymatous layer of the bark of Dictyoxylon' It is but 

 fair to add that Williamson was influenced in coming to this 

 conclusion by a discovery by Mr Nield of a piece of a large petrified 

 stem believed to be generically identical with Binney's type, 

 but subsequently referred to a distinct genus 3 , which was com- 

 parable in size with the stems responsible for Gourlie's Lygino- 

 dendron casts. The type-specimen of Gourlie's Lyginodendron 

 Landsburgii*, from Carboniferous rocks at Stevenston in Ayrshire, 

 Scotland, is represented in fig. 401. The convex areas represent 

 casts of depressions in a reticulum of cortical tissue, originally 

 occupied by comparatively delicate cells, which decayed or shrunk 

 more quickly than the enclosing framework of stronger fibrous 

 elements that remained as a prominent reticulum and produced 

 the depressions bounding the raised portions of the cast. Such 

 a cast would undoubtedly be formed by the stem on which Binney 

 founded his species: the radially disposed bands of thick- walled 

 cells seen in the outer part of the section (fig. 402) are portions 

 of an irregular anastomosing mechanical system, the reticulate 

 arrangement of which is seen in the impression of a rachis of a 

 Lyginopteris frond shown in fig. 405, E, and indicated in the more 

 slender axis reproduced in fig. 404, A, b. This reticulate form of 



1 Williamson (73) A. 2 Gourlie (44). 3 See page 186. 



4 Solms-Laubach (91) A. pp. 8, 217, 218. 



