FLORA OF THE DEVONIAN. 533 



of the species, even of the Upper Devonian, do not reappear in the 

 Carboniferous period ; but a few species extend from the Upper De- 

 vonian into the Lower Carboniferous, and thus establish a real passage 

 from the earlier to the latter flora. The connexion thus established 

 between the Upper Devonian and the Lower Carboniferous is much 

 less intimate than that which subsists between the latter and the true 

 Coal measures. Another way of stating this is, that there is a con- 

 stant gain in number of genera and species from the Lower to the 

 Upper Devonian, but that at the close of the Devonian many species 

 and some genera disappear. In the Lower Carboniferous the flora is 

 again poor, though retaining some of the Devonian species ; and it 

 goes on increasing up to the period of the Middle Coal measures, and 

 this by the addition of species quite distinct from those of the Devonian 

 pei'iod, 



3. A large part of the difference between the Devonian and Car- 

 boniferous floras is probably related to different geographical condi- 

 tions. The wide swampy flats of the Coal period do not seem to have 

 existed in the Devonian era. The land was probably less extensive 

 and more of an upland character. On the other hand, moreover, it 

 is to be observed that, when in the Middle Devonian we find beds 

 similar to the underclays of the Coal measures, they are filled, not 

 with Stigmaria, but with rhizomes of Psilophyton ; and it is only in 

 the Upper Devonian that we find such stations occupied, as in the 

 Coal measures, by SigiUaria and Calamites. 



4. Though the area to which this paper relates is probably equal 

 to any other in the world in the richness of its Devonian flora, still it 

 is apparent that the conditions were less favourable to the preservation 

 of plants than those of the Coal period. The facts that so large a 

 proportion of the plants occur in marine beds, and that so many stipes 

 of ferns occur in deposits that have afforded no perfect fronds, show 

 that our knowledge of the Devonian flora is relatively far less com- 

 plete than our knowledge of that of the Coal formation. 



5. The Devonian flora was not of lower grade than that of the Coal 

 period. On the contrary, in the little that we know of it, we find 

 more points of resemblance to the floras of the Mesozoic period, and 

 of modern tropical and austral islands, than in that of the true Coal 

 formation. We may infer from this, in connexion with the preceding 

 general statement, that in the progress of discovery very large and 

 interesting additions will be made to our knowledge of this flora, and 

 that we may possibly also learn much more of the land fauna contem- 

 poraneous with it. 



6. The fades of the Devonian flora in America is very similar to 



