LATER CRETACEOUS AND KAIXOZOIC. 197 



objection to the use of modern generic names for mere 

 leaves, and would be quite content to adopt some non- 

 committal termination, as that of "pkyttum" or "ites" 

 suggested by him. I feel, however, that almost as much 

 is taken for granted if a plant is called Corylophyllum or 

 Corylites, as if called Corylus. In either case a judgment 

 is expressed as to its affinities, which if wrong under the 

 one term is wrong under the other ; and after so much has 

 been done by so many eminent botanists, it seems inex- 

 pedient to change the whole nomenclature for so small 

 and questionable an advantage. I wish it, however, to 

 be distinctly understood that plants catalogued on the 

 evidence of leaves alone are for the most part referred to 

 certain genera on grounds necessarily imperfect, and 

 their names are therefore subject to correction, as new 

 facts may be obtained. 



The more noteworthy modern genera included in the 

 Dakota flora, as catalogued by Lesquereux, are the follow- 

 ing : Liquidambar, the sweet-gum, is represented both in 

 America and Europe, the leaves resembling those of the 

 modern species, but with entire edges, which seems to be 

 a common peculiarity of Cretaceous foliage.* Populus 

 (poplar), as already stated, appears very early in Green- 

 land, and continues with increasing number of species 

 throughout the Cretaceous and Tertiary. Salix (willow) 

 appears only a little later and continues. Of the family 

 Cupuliferce we have Fagus (beech), Quercus (oak), and 

 Castanea (chestnut), which appear together in the Dakota 

 group and its equivalents. Fruits of some of the species 

 are known, and also wood showing structure. Betula 



* With reference to this, something may be learned from the leaves 

 of modern trees. In these, young shoots have leaves often less toothed 

 and serrated than those of the adult tree. A remarkable instance is the 

 Populus grandidentatm of America, the young shoots of which have en- 

 tire leaves, quite unlike except in venation those of the parent tree, and 

 having an aspect very similar to that of the Cretaceous poplars. 



