Betula 961 



7. Betula nigra, Linnaeus. North America. See p. 988. 



Leaves greyish beneath, ovate, acute, with large serrated teeth, and six to 

 eight pairs of nerves. Branchlets glandular, tomentose. 

 *** Leaves rounded or truncate at the base. 



A. Leaves orbicular or oval. 



8. Betula corylifolia, Regel et Maximowicz. Japan. See p. 975. 



Leaves acute, pale beneath with conspicuous silky hairs on the midrib and 

 nerves ; nerves twelve to fourteen pairs. 



B. Leaves ovate-oblong, considerably longer than broad, and widest near the middle. 



9. Betula lutea, Michaux. North America. See p. 990. 



Leaves, with nine to twelve pairs of nerves, pilose on the midrib and nerves of 

 both surfaces, and on the petiole. Branchlets pilose. 



10. Betula lenta, Linnaeus. North America. See p. 991. 



Leaves with nine to twelve pairs of nerves, pilose on the midrib and nerves of 

 both surfaces ; petiole glabrescent. Branchlets glabrous, except for a few 

 hairs above the leaf-insertions. 



11. Betula utilis, Don. Himalayas, China. See p. 980. 



Leaves, with nine to twelve pairs of nerves ; lower surface with dense axil- 

 tufts of pubescence ; petiole tomentose. Branchlets tomentose. 



C. Leaves ovate, not much longer than broad, widest near the base. 



t Branchlets very glandular. 



12. Betula Ermani, Chamisso. Eastern Siberia, Manchuria, Japan. See p. 977. 



Leaves truncate at the base, with ten to twelve pairs of nerves, glabrescent 

 and conspicuously glandular beneath. Branchlets glabrous. 



13. Betula fontinalis, Sargent. Western North America. See p. 992. 



Leaves thin in texture ; rounded, truncate, or subcordate at the base, with 

 six pairs of nerves ; both surfaces minutely glandular, with scattered long 

 hairs. Branchlets with long pale hairs. 



\ Branchlets not conspicuously glandular. 



14. Betula papyrif era, Marshall. North America. See p. 983. 



Leaves about 3 inches long, with six to eight pairs of nerves ; lower surface 

 glandular and with conspicuous axil-tufts. Branchlets pubescent or 

 glabrous. 



15. Betula utilis, Don, var. Jacquemontii, Regel. Himalayas. See p. 981. 



Leaves about 3 inches long, with seven or eight pairs of nerves ; lower 

 surface glandular, with long hairs on the midrib and nerves, and without 

 conspicuous axil-tufts. Branchlets with short, erect, dense pubescence. 



1 6. Betula luminifera, Winkler. Centra) China. See p. 980. 



Leaves, 5 or 6 inches long, with ten to fourteen pairs of nerves, pubescent 

 on both surfaces. Branchlets with dense erect pubescence. 



(A. H.) 



IV 2 K 



