68 CARYOPHYLLALES 



2. ELATINACEAE. 



Elatine. 629. 

 1. Elatine triandra Schk. 

 In shallow water in ponds or creeping on muddy banks. Exeter. 



3. SALICACEAE. 



Flowers subtended by fimbriated or incised bracts, stamens usually nu- 

 merous, disc large, cup-shaped. 1. Populus. 



Flowers subtended by entire bracts, stamens usually fed often two, 

 disc minute. 2. Salix. 



1. Populus. 308. 



Leaves white tomentose beneath, lobed. P. alba. 



Leaves not white tomentose when amture, serarte or dentate. 

 Leaves broad, not much longer than wide. 



Branches erect or nearly so. P. Italica. 



Branches spreading. 

 Petioles flattened. 



Leaf-blades suborbicular, acute or short acuminate. 



5. P. tremuloides. 

 Leaf-blades broadly deltoid or cordate, abruptly long ac- 

 uminate. 4. P. sargentii. 

 Petiole terete. 1. P. balsamifera. 

 Leaves narrow, at least twice as long as wide. 



Petioles half as long as the blades or longer, abruptly long ac- 

 uminate. 3. P. acuminata. 

 Petioles one-third as long as the blades, blades lanceolate not long 

 acuminate. 2. P. angustifolia. 



1. Populus balsamifera L. 



Rare in the canons of the Hat Creek Basin. 



2. Populus angustifolia James. 

 Rare in the Hat Creek Basin. 



3. Populus acuminata Rydb. 



Rare in the northwestern part of the state. Gering. 



4. Populus sargentii Dode. Western cotton-wood. 

 Populus occidentalis (Rydb.) Britton. 



Common along streams all over the state. Lincoln; Red Cloud; 

 Stewart; Thedford; Valentine. 



5. Populus tremuloides Michx. Aspen. 

 Common in canons in the northwestern part of the state. Hat Creek 

 Basin; Valentine. 



2. Salix. 310. 



Stamens 3 or more. 



Petioles without prominent glands, trees. 



Petiole less than one cm. long, leaves narrow lanceolate, dark 

 green beneath. 1. S. Nigra. 



Petiole 1-3 cm. long, leaves broader, glaucus beneath. 



2. S. amygdaioides. 

 Petioles with prominent glands, shrubs. 3. S. lucida. 



Stamens 2. 



Leaves sharply serrate or denticulate. 



