1890.] Origin of the Plane-Trees. y 805 
have other specimefis, which will be published in my “ Monograph 
of the Flora of the Laramie Group,” in which there are all the 
variations from a sharply toothed margin with the secondaries 
entering the teeth, to an entire margin with the ends of the 
secondaries curving and arching over one another (camptodrome). 
Moreover, these differences sometimes occur in different parts of 
the same leaf. In my P. dasilobata, so far as now known, the 
nervation is always camptodrome, and the leaves strictly three- 
lobed. 
It may be well to point out in this place more specially than I 
have done hitherto that the characters last considered not only 
bear directly upon the ancient forms of the Cretaceous referred to 
Sassafras or Araliopsis, but also connect themselves with some 
of the living species, thus strengthening the argument that P. 
nobilis and P. basilobata form a sort of connecting link between 
these. Leaves of P. racemosa, for example, sometimes have very 
much the same form and general nervation of P. nobilis. Fig. 3 
represents such a leaf now in the National Herbarium, even 
showing the one strengthened secondary producing a lobe simi- 
lar to that of Dr. Newberry's figure. Otherwise it is true that 
the secondary nerves are different, but they are approached in 
some forms of P. basllobata. 
On the other hand, there is much variation in these respects 
among the Cretaceous forms referred by Lesquereux and New- 
berry to Sassafras. The margins of the lobes are generally entire, 
as in the leaf which I reproduced from the Cretaceous Flora (Pl. 
XIL, Fig. 2, of the former paper); but there are others, as, for 
example, that shown in Fig. 4 of the present paper, reproduced 
from Pl. xı., Fig. 1, of the same work, in which several of the 
outer secondaries terminate in teeth precisely as they do in P. 
nobilis. 
It remains to consider Professor Jankó’s argument from the 
geological history and distribution of the fossil species. This is 
the weakest part of his paper, as the ancient forms are so largely 
American, and American geology is so little understood in 
Europe. So far as fossil plants are concerned, it is chiefly known 
to Europeans through the works of Lesquereux, who never pre- 
