DESCRIPTION OF SPECIES. 79 
upper extremity so characteristic of the genus, and the nervation is also 
essentially the same. Hence we must conclude that the genus Lirioden- 
dron, now represented by a single species, was in the Cretaceous age much 
more largely developed, having many species, and those scattered through- 
out many lands. In the Tertiary age the genus continued to exist, but the 
species seem to have been reduced to one, which is hardly to be distin- 
guished from that now living. In many parts of Europe leaves of the 
tulip tree have been found, and it extended as far south as Italy. Its 
presence there was first made known by Unger in his Synopsis (p. 232) 
and in his Genera et Species (p. 443), where he describes it under the 
name of Liriodendron Procaccinii. Later it was mentioned by Massalongo 
(Studii FI. Foss. Senigall., p. 311) and Heer (Urwelt der Schweiz, p. 332), 
and it is enumerated and figured among the fossil plants of Iceland by Heer 
in his Flora Fossilis Arctica, Vol. I, p.151, Pl. X XVI, fig. 7b; Pl. X XVII, 
figs. 5-8; and from the Tertiary of Greenland, Vol. VII, Pork Bl 
LXXXIII. Leaves of similar form are described and figured in Heer’s 
Flora Tertiaria Helvetize, Vol. III, p. 29, Pl. CVIII, fig. 6, with the name 
of Liriodendron helveticum Fisch.; also Ettingshausen, in his Flora v. Bilin., 
Part III, p. 9, Pl. XLI, fig. 10, deseribes a fragment which he names L. 
Haueri. All these are, however, so much like the living species that it is 
impossible to distinguish them, and they should probably be united with it. 
We here have a striking illustration of the wide distribution of a species 
which has retained its characters both of fruit and leaf quite unchanged 
throughout long migrations and an enormous lapse of time. 
In Europe the tulip tree, like many of its American associates, seems 
to have been destroyed by the cold of the Ice age, the Mediterranean 
cutting off its retreat; but in America it migrated southward over the 
southern extension of the continent, and returned northward again with 
the amelioration of the climate. 
Of the species of Liriodendron found in the Dakota group of Kansas, 
the leaves of one, L. primevum Newb. (Later Extinct Floras of North 
America, etc, Ann. N. Y. Lye. Nat. Hist., Vol. IX, p. 12), are much like 
those of the living species, but considerably smaller. Another species (L. 
Meekit Heer) has small, fiddle-shaped leaves. Professor Heer considers this 
