162 Bulletin 194 



SUMMER KEY TO THE SPECIES OF ACER 



a. Leaves simple ; twigs usually without whitish bloom. 

 h. Leaf-sinuses acute at the base. 



c. Leaf-lobes long and narrow, the sides of the terminal lobe 

 diverging ; leaves silvery white beneath ; twigs rank-smelling 



when broken A. saccharinum, p. 173. 



cc. Leaf-lobes short and broad, the sides of the terminal lobe con- 

 verging; leaves not conspicuously white beneath; twigs not 

 rank-smelling when broken. 



d. Leaves distinctly white-downy beneath ; twigs appressed- 

 hairy, at least near the tip ; fruit hanging in pendulous 

 racemes, persistent on the tree until autumn ; seed portion 

 with pit-like depression on one side ; usually a shrub or 



bushy tree A. spicatum, p. 167. 



dd. Leaves glabrous or nearly so beneath ; twigs glabrous ; fruit 

 hanging in clusters, falling in early summer ; seed portion 

 without pit-like depression on one side ; medium-sized 



tree A. rubrum, p. 175. 



bb. Leaf-sinuses rounded at the base. 



r. Lower sides of leaves and petioles distinctly downy, the lobes 

 undulate or entire ; leaves very thick, drooping at the sides, 



A. saccharum nigrum, p. 171. 



cc. Lower sides of leaves and petioles essentially glabrous, the 



lobes serrate; leaves not thick, not drooping at the sides. 



d. Leaves coarsely and sparsely toothed or notched ; bark not 



longitudinally white-striped ; fruit not in racemose clusters ; 



large tree A. saccharum, p. 169. 



dd. Leaves finely and abundantly toothed ; bark longitudinally 

 white-striped ; fruit in racemose clusters ; a bushy tree or 



shrub A. pennsylvanlcum, p. 165. 



aa. Leaves compound ; twigs usually with whitish bloom, 



A. negundo, p. 177. 



