BIRCH FAMILY 65 



Trees, often very large, never shrub-like; bark ashy gray or brown, rough- 

 ened; leaves ovate, sometimes lobed, 4-7 cm. long, finely serrate, dtill 

 bronze-green, acute at the apex, truncate at the base; twigs but slightly 

 glandular-resioiferous. 8. B. montanensis. 



Twigs and branchlets more or less pubescent, not or sparingly glandular-resini- 

 ferous; shrubs or shrub-like trees. 

 Leaves oval or rhombic-ovate. 



Leaves narrowly oval or rhombic-ovate, 6 cm. long or more, sharply serrate 

 or dentate; apex acute, base cuneate; twigs finely pubescent, not glandu- 

 lar; middle lobe of the bractlets triangular, obtuse; lateral lobes rounded, 

 obUquely rhombic; fruiting aments 2-4 cm. long. 9. B. Sandbergii. 

 Leaves broadly oval, less than 4 cm. long, acute at both ends, serrate or 

 serrate-crenate; twigs pubescent and sparingly glandular; middle lobe 

 of the bractlets rounded, as broad as or broader than the ascending 

 lateral ones ; fruiting aments less than 2 cm. long. 10. B. Elrodiana. 

 Leaves obovate, rounded at the apex, cuneate at the base; twigs puberulent 

 and with scattered coarse hairs, sparingly glandular. 11. B. obooata. 

 Samara-wing narrower than the body ; shrubs mostly low. 

 Twigs and branchlets pubescent, slightly glandular. 



Leaves finely crenate or crenate-serrate, oval, acute at both ends ; twigs at first 



puberulent, at length glabrate. 12. B. crenata. 



Leaves coarsely serrate, obovate, acute or obtiise at the apex, cuneate at the 

 base; twigs with long scattered coarse hairs. 13. B. glandulifera. 



Twigs and branchlets glabrous, densely glandular-reslnlferous ; leaves obovate or 

 orbicular, crenate-serrate. 14. B. glandulosa. 



2. iLNUS (Tourn.) HiU. Alder. 



Nut bordered on each side with a- membranous wing-margin, fully as broad as the nut; 

 twigs resinous-granuliferous ; stamens 4. 

 lieaves irregularly serrate, usually very oblique at the base, slightly paler beneath. 



1. A. fruticosa. 

 Leaves incised and sharply double-serrate, green on both sides. 



2. A. sinuaia. 

 Nut merely acute-margined. 



Leaves distinctly lobed and doubly serrate; stamens 4. 



Mature leaves pubescent, especially beneath, usually glaucous beneath; bark 



white-speckled. 3. A. incana. 



Mature leaves glabrous, except on the veins beneath and in their axils, green on 

 both sides ; bark not speckled. 4. A. tenuifolia. 



Leaves not lobed, merely sinuate and glandular-dentate; stamens 1-3, usually 2. 



5. A. rhombifolia. 



Family 33. CORYLACEAE. Hazelnut Family. 



Pistillate flowers many in a cyUndric ament ; nuts small, enclosed in a bladdery bract. 



1. OSTRYA. 



Pistillate flowers few in a head-like ament; nut large, in a leaf-like Involucre. 



2. GOBYLUS. 



1. OSTRTA (Mich.) Scop. Ibonwood, Hop-hornbeam. l. O. virginiana. 



2. CORYLUS (Tourn.) L. Hazelnut. 



Twigs glabrous or nearly so; beak of the involucre fully twice as long as the nut, strongly 

 ribbed. 1- C. roslrata. 



Twigs decidedly hirsute, sometimes somewhat glandular; beak of involucre not more 

 than half longer than the nut, not strongly ribbed. 2. O. californica . 



Family 34. ULMACEAE. Elm Family. 



Fruit a samara; embryo straight. 1- Ulmus. 



Fruit a drupe; embryo with oonduplicate cotyledons. 2. Celtis. 



1. ULMUS (Tourn.) L. Elm. l- U. americana. 



2. CELTIS (Tourn.) L. Hackberrt. 



Leaf-blades neither coriaceous nor pale beneath, nor strongly rugose. w < ;• 



Leaves smooth above. i* ^- occiaentaiis. 



Leaves very rough, pustulate-scabrous above. 2. C. crassifolia. 



Leaf-blades coriaceous, strongly feticulate and rugose, paler beneath, often yellowisn 

 green. 

 Leaf-blades strongly pubescent beneath. . ^, , .^ , <, v,i j t„„*i,„j 



Pedicels 15-20 mm. long, more than twice as long as the fruit; leaf-blades toothed. 



3. C. rugulosa. 

 Pedicels 4-10 mm. long, usually less than twice as long as the frmt; leaf-blades 

 subentire *• '^^ reticulata. 



Leaf-blades glabrous beneath, or sUghtly hlspidulous on the veins and in their axils. 



5. C. Douglasii. 



