(Fig. 1218.) 



BIRCH FAMILY. 

 8. Betula nana L. Dwarf Birch. 



elula nana L. Sp. PI. 983. 1753. 

 '{. Michauxii Spach, Ann. Sci. Nat. ( II. ) 15: 195. 1841. 



A low diffuse shrub, similar to the preceding 

 cies, but the twigs glandless, pubemlent or 

 abrous. Leaves orbicular, obovate, or reniform 

 id wider than long, bright green, firm, glabrous, 

 both sides when mature, deeply and inciscly 

 renulate, rounded at the apex, rounded, obtuse 

 cuneate at the base, 3 // -io // long; petioles 

 arely more than i" long; staminate aments %'- 

 \' long, solitary or clustered; pistillate aments ob- 

 "ong, sessile or short-peduncled, erect or sonie- 

 vhat spreading, $"-$" long; fruiting bracts gla- 

 rous, the lower usually 3-lobed, the upper ovate 

 lanceolate, mostly entire; nut oblong, wingless 

 narrowly winged. 



Greenland and Labrador to Hudson Bay. Also in 

 northern Europe and Asia. May-June. 



9. Betula pumila L,. Low Birch. (Fig. 1219.) 



liet ula pit mila L. Mant. 124. i 



A bog shrub, 2- 15 tall, the twigs brown, be- 

 coming glabrous, the young foliage densely 

 brownish-tomentose. Leaves obovate, broadly 

 oval or orbicular, rounded at both ends or some 

 of them cuneate-narrowed at the base, rather 

 coarsely dentate, when mature glabrous and 

 dull green above, pale, persistently tomentose 

 or becoming glabrous beneath and prominently 

 reticulate- veined, %'-i%' long; petioles i#"- 

 3" long; fruiting pistillate aments oblong-cylin- 

 dric, erect, peduncled, i' long or less, about 3" 

 in diameter; bracts pubemlent or ciliolate, the 

 lateral lobes spreading at right angles, shorter 

 than the middle one; nut oblong, mostly rather 

 broader than its wings. 



In bogs, Newfoundland to western Ontar. 

 the Northwest Territory, south to New Jersey. Ohio 

 and Minnesota. May-June. 



5. ALNUS Gaertn. Fr. & Sem. 2: 54. pi. 9 o. 1791. 



Shrubs or trees, with dentate or serrulate leaves, few-scaled buds, and flowers of both 

 kinds in aments, expanding before, with or after the leaves, making their first appearance 

 during the preceding season, the staminate pendulous, the pistillate erect, clustered. Stam- 

 inate flowers 3 or sometimes 6 in the axil of each bract, consisting of a mostly 4-parted peri- 

 anth, 4 stamens and subtended by i or 2 bractlets; filaments short, simple; anther-sacs ad- 

 nate. Pistillate flowers 2-3 in the axil of each bract, without a perianth, but subteti.i 

 2-4 minute bractlets; ovary sessile, 2-celled; styles 2; bracts woody, persistent. 5-toothed or 

 erose. Nut small, compressed, wingless or winged. [Ancient Latin name derived from the 

 Celtic, in allusion to the growth of these trees along streams.] 



About 14 species, natives of the northern hemisphere and the Andes of South America. Besides 

 the following, some 4 others occur in the western parts of North America. 



Nut bordered by a membranous wing on each side. i. A. Alttobttuta. 



Nut acute-margined, wingless. 



Leaves obovate, broadly oval or suborbicular, dull; aments expanding long before the leaves. 

 Leaves finely tomentose or glaucous beneath. 2. A. iitcana. 



Leaves green, glabrous or sparingly pubescent beneath. 



Leaves finely serrulate; foliage not glutinous; native. 3. A. rugosa. 



Leaves dentate-serrate: twigs glutinous; introduced tree. glittinosa. 



Leaves oblong, bright green and shining above; aments expanding in autumn. 5. .-I. niarilima. 



33 



