144 Morphology BOOK i 



Sphenophyllum Dawsoni. In the same year, 1893, William- 

 son and Scott made a further study of the specimens, and 

 gave a very full account of their histology. 



Another species was described in 1895 by Solms-Laubach, 

 and was named by him Bowmanites Romeri. In 1897 

 a cone of a higher degree of organization was described 

 by Scott under the name of Cheirostrobus, and was shown 

 to be the fructification of another related genus. 



The affinities of the group gave rise at first to much 

 speculation, Schenk, Van Tieghem, and others, relying 

 partly on the similarity of certain points in its structure 

 to the stem of Psilotum, placed it near Lycopodiaceae ; 

 Stur held it to belong to the Calamarieae, Renault to 

 Salviniaceae, while Zeiller considered it to show affinities 

 with the Ophioglossaceae and the Marsiliaceae. Solms- 

 Laubach suggested in 1887 that it was sufficiently distinct 

 to form a group co-ordinate with the Lycopodiaceae, but 

 not to be included in them, a view that was advanced again 

 in 1891 by Kidston. The investigation of Cheirostrobus led 

 Scott in 1897 to hold that both it and Sphenophyllum 

 ' sprang from a very old stock which existed prior to the 

 divergence of the Lycopods and Calamarians. This common 

 stock survived for a certain time side by side with these 

 two divergent branches between them as it were. Spheno- 

 phyllum is a group which had advanced very far along 

 this third line of descent, so that its common characters 

 with the other lines have become comparatively obscure. 

 Cheirostrobus has retained more of the common character, 

 though reaching a high degree of complexity on its own lines '- 1 



The structure of Lepidodendron selaginoides was described 

 by Carruthers in 1869, but our recent knowledge of the 

 Lepidodendreae is due chiefly to Williamson, who worked 

 out the anatomy of nine distinct forms in the long series 

 of papers he contributed to the Royal Society of London, 

 1 Phil. Trans. 1896 (1897), p. 26. 



