204 ACERACEAE. 



have been given specific names indicative of their maple-like 

 foliage. Indeed it proves difficult to point out unexception- 

 able vegetative characters by which maples and viburnums 

 may be told apart with certainty, though individual species 

 are recognized readily after they have been learned. 



Some few Asiatic maples have elongated leaves that are 

 toothed but not at all lobed, and such a species as that which 

 has been named Acer car pini folium might be mistaken for a 

 hornbeam or some related shrub if attention were not paid to 

 its opposite leaves. Though the box elders appear to us pe- 

 culiar in their compound leaves, the Rocky Mountain maple is 

 trifoliolate, and certain Asiatic species not of the American 

 Negundo group, have conspicuously compound leaves. 



1. Scales 2, valvate. 2. 

 Scales more than two. 8. 



2. Buds short (scarcely 5 mm.). 3. 

 Buds large (8 mm. or more). 5. 



3. Twigs and buds glabrous. 



(Rocky Mountain maple). A. glabrum. 

 Twigs and buds puberulent. 4. 



4. Buds rather slender (2X5 mm.). 



(Mountain maple). A. spicatum. 

 Buds stouter (2.5X4 mm. Asiatic. A. argutum. 



5. Buds moderate (8 mm.) : glabrous. 6. 



Buds long (10 mm. or more), thick and blunt, glabrous. 6. 



6. Buds slender, pointed. Asiatic. A. Tschonoskii. 

 Buds stouter, blunt. 



(Striped maple). (1). A. pennsylvanicum. 



7. Twigs olive. A. rufinerve. 

 Twigs dull purplish. A. capillipes. 



8. End-bud lacking: buds short. 9. 



End-bud characteristically present or scales numerous. 12. 



9. Leaf-scars low and narrow: glabrous. 



(Japanese maple). A. palmatum. 

 Leaf-scars broad or raised in a cup, or ciliate. 10. 



