6 KKY, BASED UPON FLOWERS. 



/. Not becoming succulent in fruit ; fertile flowers 

 y. Two-three at each scale of the catkin ; calyx 



fi t Very irregularly 4-lobed, stamens 2 ; scales of cone thin and decidu- 

 ous (Betula) ; bark 



i. Brown and close, catkins erect 44. B. LENTA. 



* 2 . Yellowish-gray and ragged, catkins sub-erect 17. B. LUTEA. 



i 3 . White, and leaves 



Deltoid, smooth both sides 70. B. POPULIFOLIA. 



Ovate, hairy on veins beneath 43. B. PAPYRACEA. 



4 , Reddish-brown, shaggy 95. B. NIGH A. 



h*. Four-parted ; stamens usually 4 ; fertile scales thick, woody and 



persistent (Alnus) 163. A. RHOMBIFOLIA. 



gr 2 . Single at each scale of the catkin (Myrticacece); flowers monoe- 

 cious 164. MYRICA CALIFORNICA. 



/2. Becoming succulent in the fruit 63. MORUS RUBRA. 



e 3 . Ovary 1-celled and many-seeded, the seeds at maturity furnished with 



a hairy tuft (Salicacece) . 

 /. Bracts of the catkins entire ; calyx wanting ; stamens 2-7 (Salix) ; 



catkins 



ff. Terminating leafy branchlets; stamens 3 or more; scales of the pistillate 

 aments falling before the ripening of the fruit; leaves 

 Narrow-lanceolate, often falcate, green above and below and glabrous. 



45. S. NIGRA. 

 Ovate-lanceolate to lanceolate, pale and glaucous beneath. 



71. S. AMYGDALOIDES. 



Oblong-lanceolate to lanceolate, blue-green above pale glaucous 



beneath 140. S. LAEVIGATA 



Lanceolate, silky white both sides, glabrous above when old. 



stamens 2 46. S. ALBA VAR VITELLINA. 



</ 2 . Sessile or nearly so and peduncles mostly leafless; scales persistent under 



the fruit; leaves 

 Oblanceolate to oblong- lanceolate, dark green above paler and 



puberulous beneath 165. S. LASIOLEPIS. 



Oblong-obovate, yellowish green above 193. S. NUTTALLII. 



/". Bracts of the catkins lacerately fringed: calyx a disk-like cup; stamens 



8-30, leaves broad (Populus); styles with 

 ff. Narrow lobes; capsule small; seeds minute, petioles laterally compressed ; 



leaves 

 h. Cordate-orbicular, finely serrate 72. P. TREMULOIDES. 



71 2 . Ovate-orbicular, coarsely dentate, beneath 



Glabrous at maturity 18. POPULUS GRANDIDENTATA. 



Densely tomentose at maturity 96. POPULUS ALBA. 



71 3 . Deltoid; branchlets terete 73. P. DILATATA. 



gr 2 . Broad lobes ; capsules large ; seeds 1 line or more in length and 



leaves 

 Ovate-lanceolate, smooth, strongly reticulated and whitish beneath, 



47. P. BALSARIFERA. 



Broad-ovate, obtuse at apex, tomentose at least along the veins beneath. 



97. P. HETEROPHYLLA. 



Broad-deltoid, with laterally compressed petioles and generally 



Ten or more pairs of large crenate-serrate teeth 48. P. MONILIFEA. 



Less than ten pairs 194. P. FREMONTII. 



2 . Gymnospermee seeds naked, borne superficially on carpellary scales ; cone- 

 bearing (Conferee) ; scales 

 b. Many, imbricated, each in the axil of a bract and bearing 2 inverted ovules; 



seeds winged. 



c. Leaves evergreen, fascicled ; cones maturing the second year (Pinus). 

 ft. Leaves in 2s ; cones with scales 

 e. Smooth (awn less) ; leaves 



5-6 in. long, with long sheaths 19. P. RESINOSA. 



1 in. or thereabouts in length, sheaths short 99. P. BANKSIANA. 



e 2 . Armed with a prickle ; leaves 

 /. U-2| in. long; cones 1-3 in. 



