SPHENOPHYLLEAE 103 



We have now gained some idea of the general 

 morphology of the cone, the chief points in which are 

 the gamophyllous verticils of sterile bracts, and the 

 sporangiophores, twice as numerous as the bracts, 

 springing from their upper surface, and bearing each a 

 single pendulous sporangium at the end. The complex 

 structure of the whole strobilus is well shown in the 

 transverse section, Fig. 43, from one of Williamson's 

 drawings, and in the longitudinal section, Fig. 42. 



We will now go on to describe the structure more 

 in detail. In some specimens of vS*. Dawsoni the axis 

 is well preserved ; it is traversed by a triquetrous strand 

 of solid wood, without pith (Fig. 41, B), like that of 

 the vegetative stem in other species of the genus. It 

 was this anatomical similarity which first led Williamson 

 to regard his specimens as akin to Sphenophyllum, long 

 before Zeiller's observations proved their identity. In 

 5. Dawsoni, form a, the corners of the wood are 

 truncated, or even widely forked, and there were two 

 strands of primitive tracheae to each (Fig. 41, B, px), 

 so that the whole stele was hexarch, 1 as in some French 

 species. Associated with the cones of 5\ Dawsoni a 

 single fragment of a vegetative stem has been found, 

 showing a primary structure just like that of the axis 

 of the strobilus, but with the addition of a broad zone 

 of secondary wood and bast. There can be little doubt 

 that this specimen represents the vegetative stem of 

 Sphenophyllum Dawsoni, form a, and if so, that species 

 was evidently distinct from any other Sphenophyllum of 

 which the structure is known, though probably identical 



1 Owing to irregularities in the forking, the stele sometimes appears 

 pentarch. 



