24 LEAVES OF LIRIODENDRON HOLM. 



climates. I recall for instance the American variety of Castanea vesca, 

 the variety populifolia of Betula alba, the vnriety Canadensis of Taxus 

 /;accato,and others, of which the tj^pical forms are indigenous in Europe^ 

 and even among weeds we have several examples of that kind of vari- 

 ation, influenced by differences in climate and soil ; as, for example, 

 Alisma Plantago var. Americana, Veronica Americana but slightly dif- 

 ferent from the European species Beccabu7iga, the American varieties 

 sinuata &x\(\.iniegrifoliaoiLycopus Europwus, and the numerous varieties 

 of the Gramine(V fvom the most widely separate countries the world over. 



And if the plant shows also a liability to variation in its foliage, as 

 does our Tulip-tree, might not such kind of variation be brought 

 about in a somewhat different manner, depending on climatological or 

 terrestrial conditions? I do not think it unnatural to suppose so. But 

 a variation in this manner or as the above mentioned of a more proper 

 kind will not be considered as anything but a simple variation, at least 

 not until the changes of the specific characters have increased so much 

 after a very long space of time that the former variety becomes a 

 species, a new type. And in the same manner the varieties might be 

 supposed to belong to the original type, so that a number of apparently 

 distinct forms must be reduced to one. Do not the numerous fossil 

 Liriodendron, Sassafras, Liquidambar, Aralia, etc., favor that suppo- 

 sition "? There is, if we will now regard the fossil leaves of Liriodendron, 

 a great analogy with those of the living species, and the agreement is 

 so striking, that it seems rather hard to distinguish most of them as 

 true species, especially so when we are familiar with the recent forms. 

 Therefore has Heer in his '' Flora fossilis arctica," in the chapter en- 

 titled " Flora der Atanekerdluk"* preferred to consider some above- 

 enumerated forms as merely varieties of the species L. MeeJcii, and 

 of that reason, as he says [l. c.) : 



IcliLringe diese Formea zu einer Art, well 1) so uumerklicbe Uebergiinge zwisclien 

 demselbeu stattfinden, dass keine sicberu Greuzen zu ziebeu sind ; 2) dieselben 

 Formea ia der obem KreLde von Nebraska und Kansas Yorkominen wie in Groulaud, 

 wie ein Blick Tafel xxiii Fig, 3-G zeigt, wo ich diese amerikaniscben Bliitter zur 

 Vergleicbmig mit denen Gronlauds abgebildet babe ; 3) auch der lebende Tulpen- 

 baum mis eineu libulicbeu Formenkreis vou Bliitteru zeigt, etc., etc. 



We can not but agree entirely with him, when we regard the series 

 of leaves figured in his Flora fossilis arctica (L c.) on Plates xviii, 

 XXII, XXIII, and XL v. Among these leaves is Dr. Newberry's species 

 priniwinmi, and it seems very curious that this author should so dif- 

 fer from Heer, since he says {I. c, p. 4) not only that this species is 

 quite different from Heer's L. MeeJcii, but even that there are no 

 connecting links between them. It is now to be remarked, that the 

 mentioned leaves, figured by Heer, are from widely separated localities, 

 namely the YSiriety pirima^va from the Disco island in Greenland and 

 from Kansas, the variety genuina from Nebraska, while the two others,! 



* Oswald Heer: Flora fossilis arctica, vi, Pars ii, 1882. 

 MUd., (/.c), Plate xxii. Figs. 12 and 13. 



