RESEARCHES OX THE CARBONIFEROUS FLORA. 267 



a certainty, when, in 1884, Zeiller discovered the macro- 

 spores of a Sigillaria (47). Renault appears to be the only 

 authority who still believes in the existence of Phanero- 

 gamic Sigillaria. He continues to regard the Sigillaria' 

 leiodermaricB as Gymnosperms, while acknowledging the 

 Cryptogamic nature of the subgenus Rhytidolepis, in which 

 the existence of macrospores has been proved. He con- 

 siders the whole group as a transitional one, but for this 

 view, however interesting, there appears to be no evidence. 

 All that we actually know tends to show that Sigillaria, as 

 a whole, is a Lycopodiaceous genus with the closest 

 affinities to Lepidodendron. 



Among the fructifications of Lepidodendron described by 

 Williamson several afford excellent examples of heterospory. 

 The strobilus of L. Spencer i is especially remarkable, the 

 spores (which from their size would appear to be macro- 

 spores) being most curiously winged. This plant presents 

 several peculiarities, and it seems probable that, as its 

 discoverer suggested, it may turn out to be generically 

 distinct. 



Some of the most important parts of Williamson's work 

 on Lepidodendrea^ relate to the forms known as Halonia 

 and Ulodendron. He produced evidence which seems to 

 leave no doubt that these stems, formerly regarded as be- 

 longing to distinct genera, are nothing but the fruit-bearing 

 branches of Lepidodendron or Lepidophloios, the tubercles 

 or scars marking the insertion of the fallen cones (see espe- 

 cially mem. xix.). 



As regards the subterranean parts of the fossil Lycopods, 

 Williamson did more than any other observer to make their 

 structure known. His monograph on Stigmaria ficoides (27) 

 has been regarded by competent critics as his best work. 

 Concerning the actual structure little remains to be done, 

 but the morphology of the organs in question is still dis- 

 puted. That Stigmaria represents the underground portion 

 of various species of Sigillaria and Lepidodendron, as first 

 discovered by Binney and Richard Brown, may now be re- 

 garded as certain. Williamson always maintained that the 

 stout main axes of Stigmaria, which branch dichotomously, 



