[DM] Great allowance has to be made for the variability of leaves of the same species. The modern hazel (_C. rostrata_) is a case in point. Its leaves, from different parts of the same plant, are so dissimilar in form and size that they might readily be regarded as of different species. In the matter of names of fossil leaves, I sympathise very strongly with Dr. Nathorst, of Stockholm, in his 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 "_phyllum_" 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 inexpedient 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 following: _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.[DN] _Populus_ (poplar), as already stated, appears very early in Greenland, and continues with increasing number of species throughout the Cretaceous and Tertiary. _Salix_ (willow) appears only a little later and continues. Of the family _Cupuliferæ_ 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_ (birch) is represented by a few species, and specimens of its peculiar bark are also common. _Alnus_ (alder) appears in one species at least. The genus Plat anus (Fig. 71), that of the plane-trees, represented at present by one European and one American species, has several species in the Cretaceous, though the plane-trees seem to culminate in the early part of the succeeding Eocene, where there are several species with immense leaves. The large leaves, known as _Credneria_, found in the Cenomanian of Europe, and those called _Protophyllum_ (Fig. 72) in America, appear to be nearer to the plane-trees than to any others, though representing an extinct type. The laurels are represented in this age, and the American genus Sassafras, which has now only one species, has not one merely but several species in the Cretaceous. _Diospyros_, the persimmon-tree, was also a Cretaceous genus.