DICOTYLEDONOUS PLANTS 43 



or scale-like perianth under the bracts of the catkin. Pistil- 

 late flowers in short, erect cones. Pistil with a 2-celled ovary 

 and 2 stigmas. 



I. AI/NUS, Alder 



Trees or shrubs with broad, toothed leaves. Staminate 

 catkins long and drooping, appearing in early spring. Pistil- 

 late catkins erect, becoming dark brown and woody, persisting 

 on the trees for some time after the seeds have fallen. Stamens 

 generally 4 in each perianth. 



a. A. rhombifolia Nutt. Trees with dark brown bark. Leaves 

 ovate or oval, paler beneath, irregularly glandular-toothed. This 

 blooms very early, the staminate catkins falling in January or 

 February, and the fruit ripe at the same time. Widely distributed. 



b. A. rub'ra Bong (A. Orego'na Nutt). Bark pale gray, -mottled 

 with darker gray. Leaves ovate or elliptical, rusty-pubescent on 

 the lower surface, doubly serrate, with revolute margins to the teeth. 

 Twigs smooth, winter buds glutinous, nearly $ in. long. Catkins 

 open in the spring before the leaves. From San Francisco to Alaska. 



c. A. tenuifolia Nutt. A small tree with red-brown bark, often 

 forming thickets. Twigs pubescent. Leaves ovate rounded or cor- 

 date at base, doubly serrate with teeth acute, veins prominent, winter 

 buds short, obtuse, pubescent, about ^ in. long. In the Sierra 

 Nevada Mountains and northward, especially on the eastern slope of 

 the mountains. 



II. BET'ULA, Birch 



Trees or shrubs with smooth bark often coming off in 

 sheets, dotted on the branches. Catkins similar to those of 

 ALNUS, but the fertile ones do not persist on the trees after the 

 seeds are ripe. The scales and seeds fall away from the axis. 

 Each scale of the staminate catkins bears 3 flowers, each of 

 which consists mainly of two 2-parted filaments with an 

 anther cell on each. On every scale of the pistillate catkins 

 are borne 2-3 flowers, each of which consists simply of a 

 naked ovary with 2 diverging stigmas. 



B. occidentals. BLACK BIRCH. A tree 20-30 ft. high with 

 smooth dark brown or reddish bark, with conspicuous whitish hori- 

 zontal lenticels, becoming lighter in color with age ; the branchlets 

 dotted with resinous spots. Leaves thin, broadly ovate, serrate with 



