186 THE EVOLUTION OF OUR NATIVE FRUITS 



letin upon "The Cultivated Native Plums and Cher- 

 ries," I was unable to find any warrant for accepting 

 two species of these northern plums, although I had 

 made a studious effort to do so for several years. In 

 the meantime I have studied the plants diligently in 

 the wild and under cultivation, and have now gone 

 over much herbarium material anew, but I have been 

 utterly unable to find characters upon which to make 

 two species. The glandular character of the calyx- 

 lobes may be present or absent in the same horticul- 

 tural variety when grown in different places, and it 

 is not associated with large or early flowers, with 

 biglandular leaf -stalks or with large and flat stones 

 in the fruit. The presence or absence of two glands 

 upon the leaf -stalk is of no classificatory importance. 

 The glands are frequently present and absent on con- 

 tiguous leaves on the same tree. In the shape of the 

 stones there is the most insensible gradation from the 

 small turgid stone, which is assumed to be designative 

 of Prunus Americana, to the great flat stone of Primus 

 nigra. The accompanying illustration (Fig. 26) shows 

 this admirably. Nos. 10, 11, 12, 13, 14 are stones of 

 named varieties which Professor Sargent considers to 

 belong to Prunus nigra. All the others are forms of 

 typical Prunus Americana. One of the flattest stones 

 in the lot is No. 2, which came from a tree in cen- 

 tral New York which has most pronounced characters 

 of the extreme and typical Americana form. The 

 inventory of these stones is as follows : 



No. 1, Prunus Americana from Colorado ; 2, same 

 from central New York (stone flat, from a small very 

 early, red fruit); 3, same from Wisconsin (stone very 

 turgid); 4, same from central Michigan (small -flow- 



