WINTER KEY TO THE SPECIES OF PRUNUS 



a. Terminal bud present; bark of young trunks rather smooth, 

 b. Buds clustered at the tips of all shoots; twigs usually less 



than I /{Q inch thick ; pith of twigs brown 



P. pennsylvanica, p. 159. 



bb. Buds not clustered, or clustered only on short, spur-like 

 branchlets; twigs usually more than ^.5 inch thick; pith 

 of twigs white. 



c. Buds usually J4 mc ^ or less in length; bud-scales uni- 

 form in color, apiculate at the apex ; bark on old trunks 



blackish, rough-scaly; small to large tree 



P. serotina, p. 155. 



cc. Buds usually Y^/i inch long; bud-scales grayish on the 



\ margins, rounded at the apex ; bark on old trunks brown, 



smooth or only slightly fissured ; usually a large shrub 



P. inrginiana, p. 157. 



aa. Terminal bud absent; bark of young trunks early splitting 

 off in large, thick plates P. nigra, p. 161. 



153 



