520 Hevieu's — Prof. W. C. Williamson on Fossil Plants. 



character of the Lepidodendroid and Sigillarian stems, for " what- 

 ever else may be doubtful, there is no doubt that Stigmaria ficoides, 

 with its peculiar rootlets, is the root alike of Lepidodendron and 

 Sigillaria." With regard to these rootlets, the perusal of a very 

 important paper by M. Van Tieghem, noticing a peculiar structure 

 of the true roots of Lycopods (Sur la symmetric de structure des 

 plantes vasculaires, Ann. Scien. Nat. tome 13, 1870), led Prof. 

 Williamson to re-examine the rootlets of Stigmaria, and the results 

 are described at pp. 291-294, from which it is demonstrated that 

 " we have in each of these rootlets a single vascular bundle that 

 commences its development eccentrically in relation to the centre of 

 the rootlet to which it belongs, and that, proceeding from this one 

 pole, it is developed centripetally, the extent of that development, 

 including the number of its constituent vessels, bearing a general 

 relation to the age of the rootlet so far as is indicated by its size. 

 Excepting in the magnitude of the liber-cells, the resemblance to 

 the corresponding organs in the Selaginellece is complete. Seeing 

 that this peculiar structure only exists in the recent Lj'copods and 

 OphioglossecB, and that no other resemblance exists between the fossil 

 Lepidodendra and Sigillarice and the OphioglossecB, we must fall back 

 upon the Lycopods as the plants with which this form of rootlet 

 indicates true affinities." 



In the general conclusions respecting Carboniferous Lycopods the 

 author expresses his conviction, " that at least many of the Lepi- 

 dendroid plants acquire, through advancing age, those characteristics 

 that have hitherto been relied upon to distinguish the Sigillarian 

 from the Lepidodendroid forms," and again, it seems to have been 

 during the Paleozoic epoch that the great changes were effected 

 which caused the arborescent Lycopods to be replaced by the oolitic 

 Gymnosperms. The last section of the memoir is devoted to 

 Calamostachys and Peronosporites. With regard to the former 

 plant, considered to be allied to the Equisetacece, as all the examples 

 hitherto described possessed but one kind of spore, the examination 

 of a new specimen from the Halifax Coal-bed shows that all the 

 sporangia of the uppermost of the three fertile verticils, as well as 

 those to the right of the middle one, are filled with the small spores, 

 while the three to the left of the middle verticil, and all the four of 

 the lowermost one, contain macrospores. Prof. Williamson concludes 

 " that this discovery of macrospores and microspores in CalamostacJiys 

 Binneyana supplies another link connecting this strobilus with the 

 Lycopodiacece in the same measure that it separates the fruit from the 

 Equisetacece. That no plant belonging to the latter order ever 

 possessed both macrospores and microspores is more than we can 

 venture to affirm ; but that no living representative of the group is 

 knowu to do so is an unquestionable fact — hence to include an 

 heterosporous CalamostacJiys in the Equisetaceous order will involve 

 so large an alteration in the definition of the characteristics of this 

 order as would practically involve the creation of a new one. On 

 the other hand, this discovery strengthens my old conviction that the 

 true affinities of this strobilus are with the Lycopodiacece. The 



