TRELEASE: THE ANCIENT OAKS OF AMERICA 497 
One group only, the Paucidentatae, even remotely suggests a rain-tip 
in its acumination, but the Eocene bicornis and negundoides are some- 
what pointed, and some of the more deeply divided forms have acute 
lobes, though these do not appear to have been more than mucronate. 
One of the characters largely relied on by palaeobotanists is the 
venation of leaves. The significance of this has been insisted on by 
Oersted (10) and especially by von Ettingshausen, in the discussion 
of Quercus. Some years before his death, this distinguished Austrian 
botanist published an extensive tabular comparison of the venation 
of existing American oaks and (chiefly European) fossils ascribed to 
the same genus (11). For one interested in the Old World fossils, 
the table should be most instructive, since it often brings into asso- 
ciation a number of fossil species through comparison with a single 
living one. On the other hand, the assembling of several existing 
species through comparison with a single fossil is suggestive of re- 
semblances which might escape notice otherwise and which may indi- 
cate some sort of relationship between them. 
As a general thing, these venation associations corroborate con- 
clusions of affinity based on other considerations, as for instance Q. 
macrocarpa*' and stellata* in comparison with Q. Buchu; Q. digitatat, 
Kelloggiuit, * Leanat and rubrat in comparison with Q. cruciata; and 
Q. Douglasii* and stellata* in comparison with Q. cymaena (12). 
It is interesting to see that Q. virginiana* is brought into com- 
parison with Phellost under Q. elaena, and with imbricariat under 
Q. chlorophylla, for even good botanists have found difficulty in 
distinguishing between the leaves of some of our Southern live oaks 
and the black oaks with willow- or myrtle-like foliage. 
Less fortunate associations appear to be those in which unrelated 
species are thus brought together; e. g., Q. marilandicat and Warsce- 
wiczi* through Q. Zoroastri; Q. magnoliaefolia* and nigrat through 
Q. sinuatiloba; Q. Garryana* and ilicifoliat through Q. liriodendroides; 
Q. undulata* and Wislizenit through Q. firma; and, especially, Q. 
chrysolepis,t grisea,* lanceolata} and laurinat through Q. lauriformis. 
Though not necessarily the most abundant at any period, or the 
most typical in the Fagaceae, the most synthetic of the many leaf- 
forms shown by past and present oaks appears to me to be the sub- 
pungent or holly-like type. Those who are familiar with the existing 
Californian oaks know with what ease toothing passes into the entire 
margin in Q. chrysolepis and its allies, and into the lobed outline in 
Q. Douglasii; and it is very frequent in juvenile forms. 
Engelmann’s confidence in foliage characters was shaken by the 
1In this comparison, species of Leucobalanus are indicated by *, those of 
Erythrobalanus by t, and those of the intermediate Protobalanus by f. 
