102 THE GEOLOGICAL HISTORY OF PLANTS. 



Mr. Salter described, in 1857,* fragments of fossil wood from the 

 Scottish Devonian, having the structure of Dadoxylon, though very 

 imperfectly preserved ; and Prof. McNab has proposed f the generic 

 name Palceopitys for another specimen of coniferous wood collected 

 by Hugh Miller, and referred to by him in the " Testimony of the 

 Rocks." From Prof. McNab's description, I should infer that this 

 wood may, after all, be generically identical with the woods usually 

 referred to Dadoxylon of Unger (Arauearioxylon of Kraus). The* 

 description, however, does not mention the number and disposition 

 of the rows of pores, nor the structure of the medullary rays, and I 

 have not been able to obtain access to the specimens themselves. I 

 have described five species of Dadoxylon from the Middle and Up- 

 per Erian of America, all quite distinct from the Lower Carbonifer- 

 ous species. There is also one species of an allied genus, Ormoxylon. 

 All these have been carefully figured, and it is much to be desired 

 that the Scottish specimens should be re-examined and compared 

 with them. 



Messrs. Jack and Etheridge have given an excellent summary 

 of our present knowledge of the Devonian flora of Scotland, in the 

 Journal of the London Geological Society (1877). From this it 

 would appear that species referable to the genera Catamites, Lepi- 

 dodendron, Lycopodites, Psilophyton, Arthrostigma, Archaiopteris, 

 Caulopteris, Palmopitys, Arauearioxylon, and Stigmaria have been 

 recognised. 



The plants described by these gentlemen from the Old Red 

 Sandstone of Callender, I should suppose, from their figures and 

 descriptions, to belong to the genus Arthrostigma, rather than to 

 Psilophyton. I do not attach any importance to the suggestions re- 

 ferred to by them, that the apparent leaves may be leaf -bases. Long 

 leaf -bases, like those characteristic of Lepidofloyos, do not occur in 

 these humbler plants of the Devonian. The stems with delicate 

 " horizontal processes" to which they refer may belong to Ptilophy- 

 ton or to Pinnularia. 



In conclusion, I need scarcely say that I do not share in the 

 doubts expressed by some British palaeontologists as to the distinct- 

 ness of the Devonian and Carboniferous floras. In eastern America, 

 where these formations are mutually unconformable, there is, of 

 course, less room for doubt than in Ireland and in western Ameri- 

 ca, where they are stratigraphically continuous. Still, in passing 



* " Journal of the London Geological Society." 



f "Transactions of the Edinburgh Botanical Society," 1870. 



