496 BROOKLYN BOTANIC GARDEN MEMOIRS 



The groups which find no existing parallel in the genus may be 

 questioned as really representative of Quercus. The Fraxinifoliae 

 are not known since early Tertiary time, but they constituted about 

 1 1 percent of American Cretaceous species referred to this genus, and 

 about 17 percent in the Eocene. The Distinctae formed about 15 

 percent through the Cretaceous, Eocene and Miocene, with changing 

 species. The Suspectae constituted about 20 percent of the whole 

 in the Cretaceous, but only about 10 percent in the Eocene, and they 

 fell to some 4 percent in the Miocene. Neither of the groups that I 

 have called Myricaefoliae and Bicornes is known to have had more 

 than a small and transient representation — Q. praeundulata in the 

 Cretaceous and Q. Ramaleyi in the Miocene for the former, and 

 Q. bicornis and Q. negundoides in the Eocene for the latter; and the 

 Dallieae are represented only by Q. Dallii of the Eocene. 



The ancient foliage types more or less comparable with those of 

 today show the following relative abundance at different times, so 

 far as records go: The chestnut type, now most largely represented, 

 with nearly half the existing American species, formed one tenth of 

 the whole in the Cretaceous, over a third in the Eocene, and about 

 one seventh in the Miocene: over a fourth of the known Pleistocene 

 oaks have this kind of foliage. About 16 percent of the known 

 living American oaks have lobed leaves, and nearly half of those 

 known from the Pleistocene are of this general kind ; though about a 

 third of those known for the Miocene are of this type, none of them 

 has bristle-tipped lobes so far as I know; and in the Eocene only 

 about 3 percent are found to have had lobed leaves. The pungent 

 or holly-like type, now constituting about 4 percent of the whole 

 and represented by one form in the Pleistocene, contained about 15 

 percent of the Miocene and 9 percent of the Cretaceous forms, though 

 it is not yet recognized in Eocene deposits. As might, perhaps, be 

 expected, entire-leaved oaks, now represented by over a third of the 

 known species, have been abundant throughout the history of the 

 genus, and nearly a third of the Cretaceous, a fifth of the Eocene, and a 

 fourth of the Miocene and of the Pleistocene, species possessed this 

 type of foliage, which today is often found associated with holly-like 

 or comparably toothed leaves, often in the same species or even on 

 the same individual. 



It does not seem profitable to attempt to draw climatic inferences 

 from what I can see in these fossil oak leaves. Some ot the entire 

 leaves appear to have been rather coriaceous, as in certain semi- 

 xerophytic species now living on the Mexican table-land, and these 

 and the holly-leaved forms may have been somewhat xerophytic. 

 Most of the leaves look as if they might have belonged to mesophytes. 



