KEY TO GENERA. 
. Leaves solitary (alternate) at each node. 140. 
Leaves 2 or more at each node. 2. 
(Leaves may be represented by scales or spines or by scars 
from which they have fallen, in either of the groups). 
. Leaves characteristically 2 at each node. 15. 
Leaves characteristically 3 at each node. 3. 
(Exceptional branches may have 3 instead of 2, or 2 in- 
stead of the customary 3 leaves). 
LEAVES WHORLED. 
. Leaves reduced to small thin scales. p. 6. Ephedra. 
Ordinary leaves or their scars present. 4. 
. Leaves persistent and green (evergreen). 5. 
Leaves absent (deciduous), or dried. 10. 
. Leaves small, narrow, revolute: low shrubs. 6. 
Leaves larger, broad, flat: sap milky. 9. 
. Leaves terete: aromatic. p. 181. Ceratiola. © 
Leaves broader than thick. 7. 
. Leaves 3 or 4 in a whorl: plants erect. p. 299. Erica. 
Leaves about 5 in a whorl: plants matted. 8. 
. Leaves fiat above, not toothed. p. 180. Empetrum. 
Leaves biconvex, microscopically toothed. p. 179. Corema. 
. Stipules present: leaf-scars not fringed. p. 324. Allamanda. 
Stipules lacking: leaf-scars fringed at top. p. 326. Nerium. 
. Twigs stout: leaf-scars large. p. 341. Catalpa. 
Twigs slender. 11. 
. Buds small, often sunken in the bark. p. 344. Cephalanthus. 
Buds moderate or very evident. 12. 
. Bundle-trace 1: pods long, slender. p. 340. Chilopsis. 
Bundle-traces several. 13. 
. Pith spongy or excavated: buds acute. p. 77. Deutzia. 
Pith continuous. 14. 
. Two or four hairy lines below each node. p. 348. Diervilla. 
Without hairy ridges: buds short, blunt. p. 81. Hydrangea. 
xii er 
