262 SCIENCE PROGRESS. 



identification depended partly upon his sound estimate of 

 the anatomical characters involved, and partly on his fine 

 series of specimens. 



Our knowledge of the fructification of Sphenophyllum is 

 primarily due to Williamson, without whose researches we 

 should have no idea of its real structure. As early as 1871 

 he published a paper on " Volkmannia Dawsoni, an Un- 

 described Verticillate Strobilus from the Lower Coal- 

 Measures of Lancashire " (24), and already expressed the 

 opinion that "it is the fruit either of Aster op hyllites or of 

 Sphenophyllum" (p. $j). In memoir v. of the series in the 

 Philosophical Transactions, a fuller description of the cone 

 was given, in memoir xvii. (1890) the discovery of its 

 vegetative stem was announced, and lastly, in the following 

 year (mem. xvii.) a number of new specimens were de- 

 scribed, and all essential points in their organisation 

 explained. The strobilus consists of an axis bearing many 

 whorls of coherent bracts, from the upper surface of which 

 the numerous sporangiophores arise ; each of the latter is of 

 considerable length, and bears a single pendulous sporangium 

 at its apex. Up to this time the fossil was placed in 

 Binney's genus Bowmanites, but its affinity to Sphenophyllum 

 was always recognised by its discoverer. The full descrip- 

 tion of the structure given by Williamson enabled Zeiller in 

 1892 (46) to identify the fructification of the well-known 

 Sphenophyllum cuneifolium as being of essentially the same 

 nature, and thus to determine for the first time the true 

 character of the fruit in that genus. 



The organisation of Sphenophyllum is now as thoroughly 

 known as that of a genus of recent plants, and few fossils 

 have such indisputable claims to autonomy. The idea 

 which still sometimes finds expression, that Sphenophyl- 

 lum may represent the foliage of a Calamite, is due to 

 a confusion of thought. Certain forms of foliage in 

 some species of Sphenophyllum may doubtless bear an 

 external resemblance to some forms of Calamitean foli- 

 age, but the genus Sphenophyllum is characterised by its 

 structure and fructification, and not merely by the form of 

 the leaf. 



