SUMMER KEY TO THE SPECIES OF ULMUS 



a. Leaves essentially smooth on both sides; branches often 

 with corky, wing-like ridges; lowermost branches usually 

 short and strongly drooping; main trunk usually continuous 

 into the crown without dividing, giving to the tree a nar- 

 row-oblong outline U. racemosa, p. 129. 



aa. Leaves usually rough on one or on both sides ; branches 



4 without corky ridges ; lowermost branches not short, not 



strongly drooping; main trunk usually dividing into several 



large limbs, giving to the tree a more or less vase-shaped 



outline. 



b. Leaves usually rough above, but smooth beneath, with 

 petioles glabrous ; bark of trunk gray, deeply fissured into 



broad, scaly ridges; inner bark not mucilaginous 



U. aincricana. p. 127. 



bb. Leaves usually rough both sides, with petioles hairy; bark 

 of trunk dark red-brown, shallowly fissured into large, 

 loose plates; inner bark mucilaginous U. fuh'a, p. 125. 



122 



