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 sigifificance of this has been insisted on by 

 Oersted (lo) 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 (ii). 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. Buchii; Q. digitata\, 

 Kelloggii^, X Leana\ and rubra\ 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 Phellos^ under Q. elaena, and with imhricaria] 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. marilandica\ and Warsce- 

 wiczii* through Q. Zoroastri; Q. magnoliaefolia* and nigral through 

 Q. sinuatiloba; Q. Garryana* and ilicifolia\ through Q. liriodendroides; 

 Q. undulata* and Wislizeni^ through Q. firma; and, especially, Q. 

 chrysolepis,X grisea* lanceolata\ and laurina\ 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 



' In this comparison, species of Leucobalanus are indicated by *, those of 

 Erythrobalanus by f, and those of the intermediate Protobalanus by t- 



