cI^^p. XI.] BETULACEiE. 189 



tiov\ers in its lobes, each having two long spread- 

 ing stigmas (d). A ripe capsule is shown at e, 

 with its membranaceous wings, and the cell j 

 open to show the seed. Tlie ovary when young 

 has two cells and two ovules (as shown at ^) ; 

 but the division between the cells wastes away 

 as the seeds ripen, and one of the ovules proves 

 abortive. There are several species of Birch 

 natives of America, some of which have upright 

 oval female catkins like those of the Alder, but 

 they are always distinguished by being solitary. 

 The bark of the Birch is remarkable for its 

 tenacity, and for the great length of time that it 

 will resist decay. In America they make canoes 

 of the bark of B. papT/racea ; and in Lapland 

 huts are thatched with that of B. alba. The 

 Birch is remarkably hardy; and it grows nearer 

 the limits of perpetual snow both on mountains 

 and near the pole than any other tree. 



THE GENUS ALNUS. 



The Common Alder (Abius glutinosa) , though 

 so nearly allied to the Birch botanically, differs 

 widely in its habits ; as it always grows in low 

 marshy situations, or near water, while the 

 Birch prefers the summits of the loftiest hills. 

 In the Alder, the male catkins are long and 

 drooping, like those of the Birch ; but they are 

 generally produced in clusters of three or more 



