SUMMER KEY TO THE GENERA* 



a. Leaves simple. , 



b. Leaves needle-shaped, awl-shaped, strap-shaped or scale- 

 like, 

 c. Leaves in clusters of 2-many. 



d. Leaves in clusters of 2-5, sheathed, persistent for 



several years PINUS, p. 4. 



eld. Leaves in fascicles of 8-many, on short, lateral branch- 

 lets, deciduous in autumn LARIX, p. 17. 



cc. Leaves solitary, not clustered, 

 d. Leaves opposite. 



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

 decurrent on the stem; fruit a small, pale brown 



cone THUJA, p. 31. 



ee. 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- 



d. Leaves alternate or spirally-whorled. 

 e. Leaves flattened, soft to the touch. 



f. Leaves J^-i Y$ .inches long, sessile, aromatic; cones 

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



containing resin ABIES, p. 27. 



ff. Leaves seldom over J^ inch long, short-petioled, 

 not aromatic; cones about Y$ inch long; bark of 



trunk without raised blisters TSUGA, p. 29. 



ee. Leaves 4-sided, harsh to the touch. . . . PICEA, p. 18. 

 bb. Leaves broad and flat. 



c. Leaves alternate or clustered, never opposite nor whorled. 

 d. Margin of leaves entire or only slightly undulate. 



* See page xvm. 



