WINTER KEY TO THE GENERA* 



a. Leaves persistent and green throughout the winter, needle- 

 shaped, awl-shaped or scale-like. 



b. Leaves in clusters of 2-5, sheathed PINUS, p. 5. 



bb. Leaves solitary, not clustered, 

 c. Leaves opposite. 



d. Twigs flattened; leaves all of one kind, scale-like, 

 decurrent on the stem; fruit a small, pale brown cone 



THUJA, p. 31. 



dd. Twigs essentially terete; leaves of two kinds, either 

 scale-like, or else awl-shaped, often both kinds on the 

 same branch, not decurrent on the stem ; fruit berry- 

 like, bluish JUNIPERUS, p. 33- 



cc. Leaves alternate or spirally-whorled. 

 d. Leaves flattened, soft to the touch. 



e. Leaves /^-i/4 inches long, sessile, aromatic; cones 

 2-4 inches long; bark of trunk with raised blisters 



containing resin ABIES, p. 27. 



ee. Leaves seldom over J4 inch long, short-petioled, not 

 aromatic; cones about *4 inch long; bark of trunk 



without raised blisters TSUGA, p. 29. 



dd. Leaves 4-sided, harsh to the touch PICEA, p. 19. 



aa. Leaves not persistent and green throughout the winter, but 

 deciduous in early autumn. 



b. Twigs, branches or trunks armed with stiff, sharp prickles, 

 spines or thorns. 



c. Thorns or spines not exceeding ^ inch in length on the 

 branches, 

 d. Spines in pairs at each node; buds rusty-hairy, 3-4 



superposed ; fruit a flat pod ROBINIA, p. 169. 



dd. Spines one at each node; buds glabrous, not super- 

 posed; fruit orange-like MACLURA, p. 133. 



* See page xvm. 



xxvn 



