SUMMER KEY TO THE SPECIES OF PRUNUS 
a. Leaves oblong-ovate to obovate, abruptly acuminate at the 
apex; marginal teeth not incurved. 
b. Margin of leaves sharp-serrate with spreading teeth; 
leaves not rugose, the veins not prominent; fruit %4-% 
inch long, bright red, racemose, July-August; bark of 
trunk brown, smooth or only slightly fissured; usually a 
latgé ShPub. ncnjnasiceca cele sacs one P. virginiana, p. 157. 
bb. Margin of leaves crenate-serrate; leaves more or less 
rugose, the veins prominent; fruit about 1 inch long, 
orange-red, clustered, August-September; bark of trunk 
gray-brown, early splitting off in large, thick plates; 
4. Small tre@incuan gvisderctesa arse sees P. nigra, p. 161. 
aa. Leaves oval to oblong-lanceolate, taper-pointed at the apex; 
marginal teeth incurved. 
. Fruit light red, clustered, July-August; twigs usually less 
than 14g inch thick; pith of twigs brown; tree northern 
Uta lence ee Oise tlaea eeeaden P. pennsylvanica, p. 159. 
bb. Fruit black, racemose, August-September; twigs usually 
more than 4g inch thick; pith of twigs white; tree 
SOULRE TNs. CGe te Hae ecateeetsse sak P. serotina, p. 155. 
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