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 l /4- l /2 

 inch long, bright red, racemose, July- August; bark of 

 trunk brown, smooth or only slightly fissured; usually a 



large shrub P. virgmiana, p. 157. 



bb. Margin of leaves crenate-serrate; leaves more or less 

 rugose, the veins prominent; fruit about I indi long, 

 orange-red, clustered, August-September; bark of trunk 

 gray-brown, early splitting off in large, thick plates; 



a small tree P. nigra, p. 161. 



aa. Leaves oval to oblong-lanceolate, taper-pointed at the apex; 

 marginal teeth incurved. 



b. Fruit light red, clustered, July-August; twigs usually less 

 than }ic inch thick; pith of twigs brown; tree northern 



P. pennsylvanica, p. 159 



bb. Fruit black, racemose, August-September; twigs usually 

 more than ^/{Q inch thick; pith of twigs wihite; tree 

 southern P. serotina, p. 155. 



152 



