KEY TO GENERA. 



1. 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). 



2. 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. 



3. Leaves reduced to small thin scales. p. 6. Ephedra. 

 Ordinary leaves or their scars present. 4. 



4. Leaves persistent and green (evergreen). 5. 

 Leaves absent (deciduous), or dried. 10. 



5. Leaves small, narrow, revolute: low shrubs. 6. 

 Leaves larger, broad, flat: sap milky. 9. 



6. Leaves terete: aromatic. p. 181. Ceratiola. 

 Leaves broader than thick. 7. 



7. Leaves 3 or 4 in a whorl: plants erect. p. 299. Erica. 

 Leaves about 5 in a whorl: plants matted. 8. 



8. Leaves flat above, not toothed. p. 180. Empetrum. 

 Leaves biconvex, microscopically toothed. p. 179. Corema. 



9. Stipules present: leaf-scars not fringed, p. 324. Allamanda. 

 Stipules lacking: leaf-scars fringed at top. p. 326. Nerium. 



10. Twigs stout: leaf-scars large. p. 341. Catalpa. 

 Twigs slender. 11. 



11. Buds small, often sunken in the bark. p. 344. Cephalanthus. 

 Buds moderate or very evident. 12. 



12. Bundle-trace 1: pods long, slender. p. 340. Chilopsis. 

 Bundle-traces several. 13. 



13. Pith spongy or excavated: buds acute. p. 77. Deutzia. 

 Pith continuous. 14. 



14. Two or four hairy lines below each node. p. 348. Diervilla. 

 Without hairy ridges: buds short, blunt, p. 81. Hydrangea. 



xii 



