CHAPTER XV. 

 Arborescent Lycopodiales. 



Among the best known plants in the Palaeozoic floras are 

 the genera Lepidodendron and Sigillaria, types which are often 

 spoken of as Giant Club-Mosses or as ancestors of existing 

 species of Lycopodium and Selaginella. Of these genera, but 

 more particularly of Lepidodendron, we possess abundant 

 records in a condition which have made it possible to obtain 

 fairly complete information not only in regard to habit and 

 external features but as to the anatomical characters of both 

 vegetative and reproductive shoots. The structure oi Lepidoden- 

 dron differs too widely from that of recent Club-Mosses (species 

 of Lycopodium) to justify the statement that this prominent 

 member of the Palaeozoic vegetation may be regarded as a direct 

 ancestor of any living plant. There is at least no doubt that 

 Lepidodendron and Sigillaria must be included in the Pterido- 

 phyta. The description by Dr Scott ^ of the genus Lepidocarpon, 

 founded on petrified specimens of strobili, demonstrated the 

 existence of a type of lycopodiaceous plant in the Carboniferous 

 period distinguished from all living representatives of the 

 group by the possession of integumented megaspores, which may 

 fairly be styled seeds. Lepidocarpon and another seed-bearing 

 plant Miadesmia are described under a separate heading as 

 lycopodiaceous types characterised by an important morpho- 

 logical feature, which among recent plants constitutes a 

 differentiating character between the Pteridophytes and the 

 Phanerogams. 



