KEY, BASED UPON FLOWERS. 



e 8 . Ovary 1-2-celled with a single ovule in each cell ; 



f. Calyx scale-like or none; stigmas 2, filamentous; fertile flowers arranged 

 2 or 3 together under each scale of the cone-like catkin (Betula)\ bark 



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



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



</ 3 . White, and leaves. 



Deltoid, smooth both sides 70. B. POPULIFOLIA. 



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



f/ 4 . Reddish-brown, shaggy 95. B. NIGRA. 



f' 2 . Calyx regular and succulent in fruit 63. MORUS RUBRA. 



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



hairy tuft (Salicacece). 



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

 kins on leafy branchlets with 



g. Pallid villous dentate scales 140. S. LAEVIGATA. 



gr. 2 Yellowish deciduous scales; capsules glabrous; stamens; 3-5 petioles. 

 h. Glandular; scales of catkin entire; leaves 



Narrow-lanceolate; fruiting catkins rather dense. .45. S. NIGRA. 

 Lanceolate or ovate lanceolate, glaucous beneath, fruiting catkins 



very loose 71. S. AMYGDALOIDES 



h?. Not glandular; scales dentate 46. S. ALBA. 



/ 3 . Bracts of the catkins lacerately fringed; calyx a disk-like cup; stamens 



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



g. Narrow lobes ; capsule small ; seeds minute, petioles laterally com- 

 pressed; leaves 



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



h^ Ovate-orbicular, coarsely dentate, beneath 



Glabrous at maturity 18 POPULUS GRANDIDENTATA. 



Densely tornentose at maturity 96. POPULUS ALBA. 



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



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



leaves 

 Acuminate, smooth, strongly reticulated and whitish beneath, 



47. P. BALSAMIFERA. 



Obtuse or rounded at apex, tomentose at least along the veins 



beneath 97. P. HETEROPHYLLA. 



Broadly deltoid; branchlets angled 48. P. MONILIFERA. 



Gymncspermae seeds naked, borne superficially on carpellary scales. Cone- 

 bearing (Coniferce) ; scales 

 , 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). 

 d. Leaves in 2s ; cones with scales 

 e. Smooth (awnless) ; leaves 



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



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



e*. Armed with a prickle ; leaves 

 /. H-2i in. long; cones 1-3 in. cylindrical-ovoid when closed, oblique. 



148. P. CONTORTA. 

 / 2 . 2-3 in. long ; cone 2-2| in. long 122. P. CLAUSA. 



