SUMMER KEY TO THE SPECIES OF 

 FRAXINUS 



a. Lateral leaflets sessile F. nigra, p. 221. 



aa. Lateral leaflets petioluled. 



b. Twigs, petioles and lower sides of leaves pubescent 



F. Pennsylvania, p. 215. 



bb. Twigs, petioles and lower sides of leaves essentially glab- 

 rous. 



c. Twigs prominently 4-angled F. quadrangulata, p. 219. 



cc. Twigs terete. 



d. Lower sides of leaves essentially of the same color 

 as the upper; leaflet-margins rather finely sharp- 

 serrate F. pennsylvanica lanceolata, p. 217. 



dd. Lower sides of leaves paler than the upper; leaflet- 

 margins entire or obscurely serrate 



F. americana, p. 213. 



210 



