1902] NOTES ON THE PHYLOGENY OF LIRIODENDRON 6l 



it is certainly a very anomalous form of leaf, and repre- 

 sents the extreme of development of the lobate leaf in this 

 genus. 



We have next to consider Ward's Z. Laramie7ise. It is a more 

 recent species than any of the preceding American forms, being 

 from the Laramie. According to Stanton & Knowlton,^^ these 

 strata underlie marine Cretaceous and therefore belong to the 

 Montana formation. If this reference be correct, it leaves but 

 one American species besides the existing one subsequent to the 

 Cretaceous, If L. Laramieitse is a true species, the doubt being 

 caused by the known remains consisting of but the basal frag- 

 ment of a leaf, it was a comparatively simple form which 

 developed from the ancestral TuliptferaAikc form, which was 

 probably contemporaneous with it, although as yet no Z. 

 Ttilipifeja remains have been found in these strata. Modern 

 simple L. Tulipifera leaves similar to Z. Laramie?ise are very 

 common. 



The last fossil form to consider is the remarkable Z. Snowii 

 Lesq., from the Dakota group. It is a large leaf, ovate in outline, 

 pinnately divided into several linear, obtuse lobes on each side, 

 which are attached by their whole bases to the midrib, but are 

 entirely separated from e^ch other by a considerable interval of 

 free midrib. While it differs so widely from any of the other 

 torms of Liriodendron as to seem to represent an unallied com- 

 pound leaf, there is something about it that stamps it as a species 

 of Liriodendron. The venation is also t3^pical of the genus. It 

 ay represent a further and extreme development from Z. 

 ptnnatifidiim, which originated, flourished, and disappeared during 

 the deposition of the Dakota group; we certainly have nothing 

 like it among modern Liriodendron leaves. 



With the close of the Dakota period the Liriodendron group 

 seems to wane, having but one or possibly two species in the 

 Laramie, and none in the American Tertiary or more recent 

 formations, although the tulip tree flourished in Europe through- 

 out the Tertiary. While the extremely lobate species may have 



m 



21 



Bull. Geol. Soc. Am. 8: 127-156. 1S96. 



