206 Rhodora [DECEMBER 
- 6551-53] where it forms dense growths in places. Along with the 
typical form I observed also P. tremuloides 8. Davisiana ' [Tm. 6554] 
hitherto only known from Richmond, Ohio. 
Since the publication of this form Prof. C. A. Davis, its discoverer, 
has collected it at Wenham, Mass. It is readily distinguished by its 
large, sub-orbicular, 6-9 cm. long leaves and by its equally long, 
coarse, flattened petioles. Professor Davis has also discovered another 
very interesting form on Mount Riga, near Salisbury, Conn., for which 
the following diagnosis is proposed: 
POPULUS TREMULOIDES y reniformis. 
Differt a forma typica foliis late reniformibus, abrupte apiculatis 
margine repando serrato. 
Type in U. S. Dept. Agr. Economic Herbarium. 
Collected on Mount Riga, Conn., June 2, 1912. 
This form is readily distinguished by its kidney-shaped leaves, 
which are ordinarily about 5-6 cm. in length (including the abrupt 
point) and 7-8 cm. in width. 
There is great difference of opinion as to the limitation of Populus 
tremuloides. According to some the concept of the species embraces 
all the forms from Newfoundland to Mexico and Lower California. 
Others again regard it as a composite species, some of the constituents 
of which merit specific or at least varietal rank. The Rocky Moun- 
tain form? was segregated from the Eastern upon floral character 
mainly. The autumn coloring of the leaves differs much in the two 
forms, the one turning into a golden varying into orange, the other 
becoming pale lemon yellow. 
With the exception of the introduced Populus dilatata [P. italica] 
the Lombardy Poplar, nothing is said about our native species of 
Black Poplars (Cottonwoods) by the Maryland botanists, although 
ample material exists in the U. S. National Herbarium. The late 
Professor Ward recorded “ Populus monilifera" (P. virginiana) long 
since from the Potomac Valley, and the writer has observed it upstream 
as far as Cumberland, Md. 
The writer * has also treated the two “old” species of black poplars 
(cottonwoods) which we have in Maryland and Virginia and has 
separated them on both floral and leaf characters. Since that time 
! Amer. Midl. Nat. 2: 15, 1911. 
2 Populus aurea Tm. Am. Midl. Nat. 2: 15, ff. 3, 4, 1911. 
3 Runopona 13: 195, 1911. 
