42 KEY AND FLORA 



/. S. corda'ta Muhl. Small tree or shrub. Leaves oblong lanceo- 

 late, heart-shaped or acute at base, pointed at apex, serrate, smooth 

 except when young. Catkins leafy at base, cylindrical, lengthening in 

 fruit. Stamens 2 to each scale of the catkin. Scales dark but villous 

 with long white hairs. Capsule smooth. Style short, stigma bifid. 

 This is found on the eastern slope of the Sierra Nevada Mountains. 

 Northward. 



g. S. fluvia'tilis (S. longifolia). NARROW-LEAVED WILLOW. 

 A shrub forming dense clumps. Leaves linear to lanceolate, tapering 

 at apex and base, sessile, 2-4 in. long and ^ in. or less wide ; margin 

 entire or with scattered teeth. Catkins on leafy branchlets. Stamens 

 2 to each scale. Capsules downy or smooth, on short pedicels, with 

 large, sessile stigmas. Sometimes the leaves are smooth, sometimes 

 white downy. This is widely distributed and variable. 



II. POP'ULUS, Cottonwood, Poplar, Aspen 



Trees with broad ovate or deltoid leaves, and buds covered 

 with scales full of aromatic balsam. Staminate catkins 

 appearing before the leaves, with many stamens to each scale, 

 on a cup-shaped disk ; anthers purple, staining the ground 

 where they fall. Fertile catkins of round or ovate pods on 

 slender pedicels. 



a. P. trichocar'pa Torr. BALM OF GILEAD, BALSAM COTTON- 

 WOOD. Leaves ovate, pointed, cordate or rounded at base, crenate, dark 

 green above, greenish brown beneath, on terete petioles. Buds full of 

 balsam, and very fragrant. Tree with cracked bark and open growth. 

 Widely distributed. 



b. P. Fremon'ti Watson. Leaves broadly deltoid, with few rounded 

 teeth on the margins, bright green on both sides; petioles flattened. 

 Large tree, with gray, cracked bark. Widely distributed. 



c. P. tremuloi'des Michx. ASPEN, QUAKING ASP. Trunk straight, 

 slender, with smooth grayish white bark. Leaves round-ovate, thin, 

 on slender petioles flattened at right angles to the broad surfaces of the 

 leaf, causing it to sway edgewise with the least perceptible breeze. In the 

 Sierra Nevada Mountains and far northward. 



BETULA X CE^E. BIRCH AND ALDER FAMILY 



Monoecious trees or shrubs, growing along streams. Leaves 

 toothed. Staminate catkins drooping ; when young covered 

 with resin, but without bud-scales. Stamens 2-4 in a 4-lobed 



