DESCRIPTION OF SPECIES. 47 



Fig. 5, and as the basilar pair of nerves close to tlie borders is present, the 

 identity of these leaves may be admitted. 



There is the same degree of difference between tlie two leaves referred 

 to this species here and in the illustrations of Dr. Newberry. One (PI. iii, 

 Fig. 6) is larger ; the lower pair of secondaries is at a distance from the base 

 of the leaves; the lower secondaries are opposite, and there is still on one 

 side a short thinner basilar nerve, while in the leaf of PL ii. Fig. 1, which 

 is smaller, the lowest lateral nerves join the midrib quite near tlie basal 

 border of the leaf, and there is no basilar nerve underneath. In tliis leaf, 

 moreover, the borders are entire and the nerves camptodrome, while in tlie 

 other the upper border of the leaf appears crenulate, and the nerves reach 

 the borders as craspedodi'ome. From this it appears that, with a slight 

 modification, Heer's description of the species is exact, the difference being 

 merely the result of varieties in the different leaves. Schimper says, how- 

 ever, in his description of these leaves, that they are coarsely dentate above 

 (superne grosse dentatis), which is apparently a mistake. I. have seen, how- 

 ever, more recently, a number of leaves with dentate borders (not coarsely 

 dentate) having the same kind of nervation as the leaves figm-ed in our 

 Pis. VII and VIII, and also the same size and form. 



They appear to constitute a variety of the species, as Populits lifif/iosa 

 var. dcHticidata. But this does not prove that the leaf described by Heer as 

 P. litigiosa nor those referred to it by Dr. Newberry and by myself pertain 

 really to Populus, the nervation being generally craspedodrome and pin- 

 natifid. 



Habitat: Commonly found in the Dakota Groi;p of Kansas and 

 Nebraska. No. 4050, from Pipe Creek, Cloud County, Kansas, and No. 

 4138, from ten miles northeast of Delphos, Kansas, of Mr. R. D. Lacoe's 

 collection. Fig. 1, PI. LIX, from Fort Marker, Kansas, is No. 2770 of the 

 U. S. National Museum. 



POPULITES ELEGANS Lesq. 



PI. XLVI, Fig. 5; PI. XLVII, Figs, li, 3. 

 Cret. Fl., p. 69, PI. in. Fig. 3. 



The description of the species as it has been establislieil in Cret. Fl. 

 should be completed by the addition of the word dentate to the character of 

 the borders, which indeed are as often dentate or undulate as entire. I have 

 also to remark that the areolation of the leaves referable to this species 

 appears more distinctly marked and that the leaves of Populus Ut'ujiosa Heer 



