12 SPRING FLORA 



6. P. angustifolia James. Narrow-leaved Cottonwood. A 

 slender tree (sometimes reaching- a height of 70 ft.) with 

 ascending- branches and gray twigs. Leaves lanceolate, lance- 

 olate-ovate or ovate; acute or acuminate or some obtuse; finely 

 crenulate; short-petioled (much resembling willow leaves in 

 general appearance). Capsules ovoid, short-pedicelled. Along- 

 mountain streams. April-May. 



7. P. acuminata Rydb. Much like the last, but the leaves 

 are more rhomboid-lanceolate, are abruptly long-acuminate, 

 and are long-petioled. 



BETULACE^l. Birch Family. 



Monoecious shrubs or trees with slender branches. 

 Leaves simple and alternate, with deciduous stipules. 

 Staminate flowers in catkins ; pistillate ones in clusters, 

 spikes or scaly cone-like catkins. Stamens 2-8; stig- 

 mas 2. Ovary 2-celled, ripening into a winged or 

 wingless nut. 



Pistillate inflorescence persistent 1. Alnus 



Pistillate inflorescence deciduous 2. Betula 



1. ALNUS. Alder. 



Shrubs or trees growing near streams. Flowers developed 

 before or with the leaves. Staminate catkins long and droop- 

 ing, with 3 flowers to each scale. Stamens 3-6 (usually 4). 

 Pistillate catkins ascending-, at length erect; their bracts 

 becoming woody and cone-like, and remaining on the tree 

 through the winter. Fruit with or without wings. 



1. A. tenuifolia Nutt. "(A. incana yirescens S. Wats.) A 

 small tree (8-20 ft. high), the trunk with greenish-gray bark, 

 and branches reddish -brown. Winter-buds obtuse. Leaves 

 ovate, sharply double-toothed; light-green and smooth on 'both 

 sides or slightly pubescent; strongly veined. Flowers pro- 

 duced early in spring before the leaves; the catkins are 

 developed from terminal naked buds of the preceding year's 

 growth. Peduncles shorter than the "cones." Bracts of both 

 inflorescences dark-red while in bud; the fertile ones becoming 

 light-brown in fruit. Seeds with thin membranous margins. 

 March-April, 4,800-9,000 ft. 



2. BETULA. Birch. 



Smooth-barked shrubs or slender trees growing 1 near 

 streams. Staminate catkins sessile; long: and drooping; the 

 flowers usually 3 to each scale of bract; each flower consisting 

 of a scale-like and shield-shaped calyx, which bears 2 2-forked 

 filaments. Each fork of filament bears an anther-cell. Pis- 

 tillate catkins cylindrical to ovoid, erect; flowers 2-3 to each 

 3-lobed bract, with neither calyx nor bractlets; the bracts 

 dropping away from their axis as soon as seeds are mature. 



1. B. fontinalis Sargent. (B. microphylla Bunge.) Black 

 Birch. Shrub or slender tree 9-20 ft. high, with reddish-brown 

 bark conspicuously marked with whitish, horizontal lenticels 

 and with glandular-warty drooping branches. Leaves broadly 

 ovate; sparingly pubescent; serrate with glandular teeth. 

 April-May, 4,600-8,000 ft. 



