SPHENOPHYLLEAE IO i 



cases where it was possible to count them. It has not 

 yet been decided for certain whether the bracts of succes- 

 sive whorls were alternate or superposed ; though the 



br 



Fig. 41. — Sphenophyllwn Dwwsoni. A. Diagram of cone in longitudinal section, showing 

 three whorls, ax, axis ; br t bracts ; sj>, sporangiophores ; sm, sporangia ; br*, whorl 

 of bracts seen from the inside in surface view. (G. T. G.) B. Stele of axis, in trans- 

 verse section. Wood only preserved. J>x, protoxylem-groups, of which there are 

 six in all ; p/z, remains of phloem. X about 20. Will. Coll. 1049. C. Spores, in 

 superficial aspect. X about 100. B and C after Williamson, Phil. Trans. 



analogy of the vegetative leaves would lead one to 

 expect superposition, the direct evidence is in favour 

 of an alternate arrangement. The sporangia were 



