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1. POPULUS. Poprtar or CotTronwoop. 
Petioles terete; ovary tomentose. 1. P. trichocarpa. 
Petioles flattened; ovary glabrous. 
Leaves coarsely serrate-dentate; capsules globose; stigma-lobes dilated. 
2. P. Fremontii. 
Leaves finely crenate-serrate; capsules oblong-conic; stigma-lobes linear. 
3. P. tremuloides. 
1. Poputus TRicHocarpa Torr. & Gray; Hook. Ic. Pl. 9: 9/. 878. 
1852. 
Type locality: “Santa Clara River, near Beneventano [Ven- 
tural, California.” 
Distribution: British Columbia and western Montana, south- 
ward throughout California. The mountain forms often develop 
narrow leaves that approach P. angustifolia, but there seem to be 
no stable characters that warrant their separation as a distinct 
variety or species. In southern California this species occurs 
in the Upper Sonoran on the coastal slope, and in the Transition 
and the lower altitudes of the Canadian Zones. In the Lower 
Sonoran of the interior valleys, at San Diego, and on the deserts, 
it is replaced by P. Fremontit. 
Specimens examined: Sulphur Mountain Spring, near Santa 
Paula, Abrams & McGregor 58; Monrovia Canyon, San Gabriel 
Mountains, Dudley, Nov. 20, 1907; Bear Valley, San Bernardino 
Mountains, Abrams &F McGregor 738. 
2. Poputus Fremontu S. Wats. Proc. Am. Acad. 10: 350. 1875. 
Type locality: “On Deer Creek at ‘Lassen’s’ in the upper 
Sacramento Valley.” 
Distribution: Sacramento Valley south to northern Lower Cali- 
fornia, and eastward to southern Colorado and western Texas. 
In southern California this species occurs along most of the streams 
of the interior valleys, approaching the coast in San Diego County; 
it is also abundant in the canyons on the desert slopes of all the 
mountains. A form with pubescent twigs, foliage, and peduncles, 
which occurs on the delta of the Colorado River, may prove worthy 
of recognition when more complete material is at hand. My own 
specimens from Elsinore Lake are fully as pubescent as the delta 
plants, but specimens from Cajon Pass (Abrams &9 McGregor 695) 
are only sparsely so, thus approaching the typical form which is 
glabrous. 
