WINTER KEY TO THE SPECIES OF POPULUS 



a. Branches erect, more or less appressed to the main stem, 

 forming a narrow, spire-like crown. ..P. nigra italica, p. 59. 

 aa. Branches spreading, forming a broad crown, 

 b. Terminal buds %-^A i ncn long, not resinous. 



c. Buds and twigs more or less conspicuously white-downy ; 



twigs green P. alba, p. 47. 



' cc. Buds and twigs not conspicuously white-downy; twigs 

 usually red-brown. 



d. Terminal buds about % inch long, puberulous, dusty- 

 looking; lateral buds widely divergent; twigs rather 



coarse P. grandidentata, p. 51. 



dd. Terminal buds about J4 mcn l n g> glabrous, lustrous ; 

 lateral buds more or less appressed; twigs rather 



slender P. tremuloides, p. 49. 



bb. Terminal buds l /2-i inch long, sticky-resinous. 



c. Terminal buds about l /2 inch long; buds not fragrant; 



twigs usually yellow, more or less strongly angled 



P. deltoidcs, p. 57. 



cc. Terminal buds nearly i inch long; buds fragrant; twigs 



usually red-brown and seldom strongly angled 



P. balsamifera* p. 53. 



P. candicans* p. 55. 



*It is difficult to distinguish between these species in the 

 absence of summer characters. If leaves can be found on or 

 beneath a tree which is sufficiently segregated from similar trees 

 as to avoid any chance for error, the summer key on the. opposite 

 page may be used. 



45 



