469 
the period of greatest development of the genus, in cretaceous 
times.» The particular species with which this. paper has to do is 
of importance for the reason that only one other Liviodendren, and 
that an imperfect specimen, has been described from the Laramie 
group (L. Laramiensis Ward, Bull. No. 37, U. S. Geol. Surv. 102, 
pl. 48, f. 2), and also because our species possesses the unique 
characteristic of a winged petiole. Leaving this feature to be dis- 
cussed further on, attention is now called to the significance of the 
leaf forms. 
From the standpoint of the evolutionist the development of 
the individual is the epitome of the development of the type, so 
_. that we ought to find some traces of the ancestry of the genus in 
the successive leaf development of our living tulip tree. This 
‘spect of the subject has been commented upon by several of the 
authors Previously mentioned, but their works were prepared pre- 
Vious to the issue of Lesquereux’s posthumous “Flora of the Da- 
kota Group” (Monog. No. 17, U. S. Geol. Surv., 1892), and the 
§teat development of the genus there brought out was not known 
to the writers; neither, of course, was the species which is de- 
scribed in this paper, so that many points of significance were 
_ Missed by them : 
During the present year I made a series of observations upon 
and collected a number of specimens of leaves from seedlings, 
Saplings, shoots from old stumps, and the branches of mature trees. 
ey, of course, vary exceedingly, but by regarding the series as 
_ * whole it will be seen that there is a most striking parallelism 
tween the entire or merely undulate margins of the leaves from 
the seedlings and young shoots and the earliest fossil forms, re- 
Presented by ZL. simplex, L. primevum, etc., while it is in the 
ves of the more mature branches that the lobing becomes of 
Sufficient Prominence to compare them with later forms like Z. 
SBanteum, L, acuminatum, etc. 
The significance of the wing-like appendages to the petiole 
May now be considered. Similar appendages have been noted in 
, ‘tT genera, and we are indebted to Prof. Lester F. Ward for 
-javing presented the case of Platanus (« Palzontologic History of 
> © Genus Platanus,” Proc. U.S. Nat. Mus. 11: 39-42, p/. 17-22 ; 
; ‘Origin of the Plane-Trees,” Am, Nat. 24: 797-810, pl. 28), and. 
. 
