165 



THE PLUMS AND CHERRIES PRUNUS, (Tourn.) Linnaeus. 



This genus comprises about 90 species well distributed over the 

 north temperate zone and locally in the tropics. A large number 

 of the representatives are found in North America. Seven species 

 are native to Pennsylvania and 4 foreign species have been extensively 

 naturalized. Only 4 of the native species are described on the fol- 

 lowing pages. The other native species are Porter's Plum (Prunus 

 alleghaniensis), Appalachian Cherry (Prunus cuneata), and the Sand 

 Cherry (Prunus pumila). 



Among the introduced species which have been cultivated exten- 

 sively are the Domestic or Sweet Cherry (Prunus avium), the Sour 

 Cherry (Prunus Cerasus), the Perfumed Cherry (Prunus Mahaleb), 

 and the Peach (Prunus Persica). The latter was introduced from 

 Asia and the others from Europe. 



SUMMER KEY TO THE SPECIES. 



Page. 

 1. Flowers in racemes terminating leafy branches, hence appearing after the leaves 2 



1. Flowers in umbels developing from lateral buds before or with the leaves, 3 



2. Leavos thickish, oblong or oblong-lanceolate, taper-pointed, serrate with short 



incurved stout teeth; inner bark aromatic P. serotina 166 



2. Leaves rather thin, oval to obovate, short-pointed, very sharply serrate with some- 



what spreading slender teeth; inner bark with a rank disagreeble odor, P. virginiana 167 



3. Flowers small; fruit small, borne in clusters; branches not thorny or armed, 



P. pennsylvanica 168 

 3. Flowers large; fruit large borne singly; branches often thorny or armed, P. americana 169 



WINTER KEY TO THE SPECIES. 



1. Terminal buds absent, P. americana 169 



1. Terminal buds present, 2 



2. Buds clustered at the tips of the twigs; twigs rather slender usually less than 1/16 



of an inch in thickness, P. pennsylvanica 168 



2. Buds rarely clustered and if clustered only on stubby lateral spurs; twigs relatively 



stout, usually over 1/16 of an inch in thickness, 3 



3. Medium to large tree; bark on old trunks black and rough; buds relatively small 



with uniformly-colored scales sharp-pointed at apex, P. serotina 166 



3. Small tree to shrub; bark on old trunks brown and rather smooth; buds relatively 



large with grayish- margined scales rounded at the apex P. virginiana 167 



