98 THE GEOLOGICAL HISTORY OP PLANTS. 



It thus appears that we already know five species of Coniferous 

 trees of the genus Dadoxylon in the Middle Erian of America, an 

 interesting confirmation of the facts otherwise known as to the 

 great richness and variety of this ancient flora. The late Prof. 

 Goeppert informed me that he had recognised similar wood in the 

 Devonian of Germany, and there can be no doubt that the fossil 

 wood discovered by Hugh Miller in the Old Red Sandstone of Scot- 

 land, and described by Salter and McNab, is of similar character, and 

 probably belongs to the genus Dadoxylon. Thus this type of Conif- 

 erous tree seems to have been as well established and differentiated 

 into species in the Middle Devonian as in the succeeding Carbonif- 

 erous. 



I may here refer to the fact that the lower limit of the trees of 

 this group coincides, in America, with the upper limit of those prob- 

 lematical trees which in the previous chapter I have named Proto- 

 gens (Nematophyton, Celluloxlyon* Nematoxylon ]), though Apo- 

 roxylon of Unger extends, in Thuringia, up to the Upper Devonian 

 (Cypridina schists). 



v. — Scottish Devonian Plants op Hugh Millek and others. 

 (Edinburgh Geological Society, 1877.) 



Previously to the appearance of my descriptions of Devonian 

 plants from North America, Hugh Miller had described forms from 

 the Devonian of Scotland, similar to those for which I proposed the 

 generic name Psilophyton; and I referred to these in this connection 

 in my earliest description of that genus.:]: He had also recognised 

 what seemed to be plants allied to Lyoopods and Conifers. Mr. 

 Peach and Mr. Duncan had made additional discoveries of this kind, 

 and Sir J. Hooker and Mr. Salter had described some of these re- 

 mains. More recently Messrs. Peach, Carruthers, and McNab have 

 worked in this field, and still later* Messrs. Jack and Etheridge 

 have summed up the facts and have added some that are new. 



The first point to which I shall refer, and which will lead to the 

 other matters to be discussed, is the relation of the characteristic 

 Lepidodendron of the Devonian of eastern America, L. Gaspianum, 

 to L. nothum of Unger and of Salter. At the time when I described 

 this species I had not access to Scottish specimens of Lepidodendron 



* " Journal of the Geological Society," May, 1831. 

 •f Md., vol. xix, 1863. 



I " Journal of the Geological Society," London, 1859. 



* Ibid., 1811. 



