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 
SAGER OE PSSR ASS ea URE SU Rate Sa 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: Dlwisliveave.cs cagesee ss taa.en JUNIPERUS, p. 33. 
cc. Leaves alternate or spirally-whorled. 
d. Leaves flattened, soft to the touch. 
e. Leaves 14-114 inches long, sessile, aromatic; cones 
2-4 inches long; bark of trunk with raised blisters 
CONTAINING’ FES oadirrs jee esa eemess ABIES, p. 27. 
ee. Leaves seldom over ¥% inch long, short-petioled, not 
aromatic; cones about 34 inch long; bark of trunk 
without raised blisters.............. TSUGA, p. 29. 
dd. Leaves 4-sided, harsh to the touch..... PICEA, p. 109. 
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 xviii. 
— XxvII — 
