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 %-%4 inch long, not resinous. 
c. Buds and twigs more or less conspicuously white-downy ; 
EWISS PLCC aes 24's ss. sh COMA EE P. alba, p. 47. 
ce. 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) cidchua- vias e ew eteed ia P. grandidentata, p. 51. 
dd. Terminal buds about inch long, glabrous, lustrous; 
lateral buds more or less appressed; twigs rather 
Slen@ers ave edentciaplide ye eee xe P. tremuloides, p. 49. 
bb. Terminal buds %4-1 inch long, sticky-resinous. 
c. Terminal buds about ¥%4 inch long; buds not fragrant; 
twigs usually yellow, more or less strongly angled 
iia A wd eed ay da Siac lets eae de P. deltoides, p. 57. 
cc. Terminal buds nearly 1 inch long; buds fragrant; twigs 
usually red-brown and seldom strongly angled 
ide tessa elate Mask Be Ga Re eb aseneisede P. bdlsamifera,* p. 53. 
P. candicans,* p. 55. 
*Tt 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. 
ay | ee 
