58 



by the outline of its coriaceoas leaves and still more by their nervation ; 

 two species of Magnolia, represented by a large number of leaves and 

 recognized already in the FliylUtes by Heer, and three species of Lirio- 

 dendron, the tulip tree, whose form of leaves like that of the Sassafras 

 sufficiently jiroves the generic reference. 



Considering these genera separately in regard to their relations and 

 to their present and past distribution, we UndAralia still represented in 

 our flora by six species, all of different characters of leaves. For indeed 

 the relation of the fossil form is rather to an old section of the Aralia 

 with compound palmate leaves, now referred to the Hedera like H. Xal- 

 apensis of the mountains of Mexico. This type is still represented by 

 large leaves in the Pliocene flora of California. Hedera helix, the ivy to 

 which our Cretaceous species H. ovalis is closely allied, is indigenous of 

 Europe, where its origin is confirmed by paleontology, the species having 

 been recognized in the Pliocene of Italy. It is, however, of so easy 

 acclimation with us that it looks like an old wanderer returned home 

 after a long absence. In the temperate zone of the United States, it 

 invades walls and stone-dwellings as it covers the ruins of the Euro- 

 pean castles of old. The genus Aralia is not represented yet in the 

 fossil Tertiary flora of Europe. 



But evidently these two most admirable genera of trees, Magnolia 

 and Liriodendron, belong to ISTorth America by origin, succession, and 

 presence. Of the eight species of true Magnolia, (Magnoliastrum,) now 

 known to botanists, seven belong to the western slope of the temperate 

 zone of North A merica, and the other M. Mexicana, is either a variety 

 of M. glauca, or M. grandiflora, or even is referable to a different genus. 

 We have seen that already two species of Magnolia have been recog- 

 nized by Heer in the Dakota group. I have added two species to the 

 number, one of which, however, is of uncertain affinity. In our lower 

 Tertiary, the Eocene, we have still seven species; five of them in 

 the Mississippi Eocene, one at Carbon, and one at Black Butte. Of 

 the Mississippi species, two have been fonnd in the Eaton Mountains, 

 New Mexico, marking thus the genus with the same climatic distri- 

 bution as it has now,- or with wandering representatives far from 

 the limits of its area of general distribntion. Thus, one of the species 

 M. Inglefeldi, found at Black Butte, is described by Heer from the 

 flora of Greenland, just as we find now groups of M. glauca and M. um- 

 brella, isolated in deep gorges of Pennsylvania, far out of their mean 

 range of habitat. Li the Pliocene of California the genus has two spe- 

 cies. In the Tertiary formations of Europe it has none. As remarked 

 above, however, one species is described from Greenland, and two from 

 the Cretaceous formation of Moletin, these of a type different from that 

 of the Dakota group species. 



Liriodendron, the tulip tree, has in its characters, its distribution, and 

 its life a great degree of affinity with Magnolia. The American 

 species is the only one known now in the vegetable world, and its habitat 

 is strictly limited to this country. It does not ascend higher than the 

 fortieth degree of latitude, except, perhaps, casually, like Magnolia 

 under the protection of favorable local circumstances. The genus does 

 not appear to have any disposition to modifications of its type and to 

 migrations. We have not as yet any fossil remains of it in our Tertiary 

 formations. In that of Europe it is represented from Greenland to Italy 

 by one species only. The leaves of diiferent forms described from 

 the Dakota group as four species, may perhaps be referable to 

 a single one, as the characters, especially the size of the leaves, may 

 be local and result from climatic circumstances. It has thus passed 



