BOTANY: W, TRELEASE 
629 
(perhaps two distinct species) in Eocene and Miocene deposits, and that 
what has been taken for the existing Q. chrysolepis — the type of the 
subgenus Protobalanus — occurred in the Miocene; but this identifica- 
tion might well be questioned by a critic. A proper understanding of 
the affinities of existing groups of species undoubtedly calls for a just 
appreciation of their connection with these ancestral forms. This I do 
not profess to have formed. I find the occurrence of a few aberrants — 
among them the South American species — in the subgenus Erythro- 
balanus puzzling, but can see no satisfactory evidence that red- or 
black-oaks are recognizable in any of the older fossils; and the group 
is certainly exclusively American today. Notwithstanding this, a 
resemblance is observable between the white oaks of Europe and those 
of western rather than eastern America, that proves puzzling. 
On the whole, I am unable to trace any existing groups to those of 
Tertiary time. Pleistocene species, of which 18 are recognized for the 
United States, as is to be expected are scarcely different from those of 
today, though they are sometimes given distinctive names. In the 
early Pliocene should be sought definitely recognizable ancestral forms 
of these and their living descendants. 
Considering the multitudinous — and in their extremes very diverse — 
types of such an existing assemblage as that of the Rocky Mountains, 
in which Engelmann and other excellent botanists have been unable to 
see more than a single polymorphic species, and the comparable range — 
to which the keen von Ettingshausen refers the manifold European 
oak types of today — in the fossil Q. Palaeo-Ilex, I am unable to see that 
all of the existing American oaks may not have descended from a sin- 
gle synthetic type of this kind, such as the Miocene species that has been 
held to be identical with the existing intermediate oak Q. chrysolepis. 
Out of this type, rightly or wrongly, I have built the present divergent 
branches of white and red oaks as I understand their affinities, behev- 
ing that the European and American white oaks have no direct connec- 
tion and that on each continent the manifold and often parallel forms of 
today have been independently derived from distinct late Tertiary 
types not closely related to one another in descent. 
