S. Watson—Poplars of North America. 1385 
Art. XX.—The Poplars of North America; by SERENO 
WATSON. 
THE following incomplete synopsis of the species of Populus 
is based upon the material in several of our principal herbaria, 
and is published for the purpose of drawing the attention o 
botanists during the coming season to this still very imperfectly 
known genus. Flowers and fruit even of the common species 
are too rare in collections, and are much needed for their satis- 
factory definition. 
§ 1. Styles two, with two or three narrow or filiform lobes: 
capsules small, thin, oblong-conical, two-valved: seeds very 
small: leaves ovate. 
* Petioles flattened: bracts silky: stamens six to twenty. 
1. P. tremuloides Michx. 2. P. grandidentata Michx. 
** Petioles terete: bracts not silky: stamens twelve to sixty. 
3. P. heterophylla L. 
. Styles two to four, with dilated lobes: capsules large, 
often thick, subglobose to ovate-oblong, two to four-valved : 
bracts mostly glabrous. 
* Leaves cordate or ovate to lanceolate, crenate; petioles 
terete: stamens twelve to thirty: seed a line lon 
4. P. balsamifera L. Leaves whiter beneath, ovate-lanceo- 
late, acuminate, glabrous ; petioles one-half to two inches long, 
thombie-ovate to narrowly lanceolate, mostly cuneate at base, 
often small ; petioles one-half inch long or less (rarely one 
