20 Bulletin 194 



WINTER KEY TO THE GENERA 



a. Leaves persistent and green through the winter, needle-shaped, 

 awl-shaped or scale-like. 



b. Leaves in clusters of 2-5, sheathed Pinus, p. 25. 



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. 51. 

 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. 53. 

 cc. Leaves alternate or spirally-whorled. 

 d. Leaves flattened, soft to the touch. 



e. Leaves ^-1/4 inches long, sessile, aromatic; cones 2-4 

 inches long; bark of trunk with raised blisters containing 



resin Abies, p. 47. 



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

 matic; cones about ^ inch long; bark of trunk without 



raised blisters Tsuga, p. 49. 



dd. Leaves 4-sided, harsh to the touch Picea, p. 37. 



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

 ciduous in early autumn. 



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

 thorns. 



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

 branches, in pairs at each node; buds rusty-hairy, 3-4 super- 

 posed ; fruit a flat pod Robinia, p. 159. 



cc. Thorns or spines much exceeding Yz inch in length on the 

 branches, not in pairs at each node ; buds not rusty-hairy, not 



superposed ; fruit a pome Crataegus, p. 147. 



bb. Twigs, branches or trunks unarmed. 



c. Leaf-scars mainly crowded on short, stout, lateral shoots; 



bundle-scar 1 ; fruit a cone Larix, p. 35. 



cc. Leaf-scars distributed along the lateral branches ; bundle-scars 

 3-many ; fruit not a cone. 

 d. Leaf-scars 2 at a node, i. e., opposite. 



e. Terminal buds 3^-1^ inches long, resin-coated; twigs 

 very stout Aesculus, p. 179. 



