32 Agricultura-l Experiment Station, Ithaca, N. Y. 



tute probably the hardest knot in American pomology. The 

 botanical status of the native plums is equally unsatisfactory, and 

 the group is one of the most inextricably confused of any one of 

 equal extent in our whole flora. There are few botanical features 

 which are reliable in the characterization of the species, and the 

 specimens which are preserved in the leading herbaria are few 

 and unsatisfactory. There is probably no group of American 

 plants in which the characters of growing trees and fresh fruits 

 are more essential in the distinguishing of species than in these 

 plums. Yet there are the most remarkable variations in habit of 

 tree, seasons of blooming and ripening, size, flavor and texture 

 of fruit, and characters of stone, even among varieties coming 

 presiunably from the same species. Fully half of the varieties 

 now in cultivation were picked up in woods and copses and trans- 

 ferred to the orchard, and the variations between these varieties 

 are fully as great as between those of known or garden origin. 

 There is evidence that hybridity is responsible for some of the 

 variation of cultivated forms, but whether it takes place in nature 

 Is wholly a matter of conjecture. It is an unsafe principle to 

 invoke the aid of hybridity, upon purely speculative grounds, to 

 explain doubtful points; and I have therefore referred doubtful 

 forms directly to the most closely aUied species or type, so far as 

 IX)ssible, leaving si)eculations as to their true affinities to future 

 students. The native plums can be commended with confldence 

 to any one who desires to study contemporary evolution. 



In the following study, which has now extended through six 

 years, I have had the co-operation of many botanists and horti- 

 culturists. I am under especial obligations to all those whose 

 names are mentioned in this paper, particularly to J. "W. Kerr, 

 Denton, Maryland, and T. V. Munson, Denison, Texas. Without 

 the aid given by these last two persons the preparation of this 

 monograph would have been impossible. Mr. Kerr probably has 

 the largest growing collection of native plums in existence, and I 

 have had the advantage of a personal inspection of his orchards 

 in the fruit season. I have had access to the herbarium collections 

 at Harvard University, (Columbia College, Department of Agri- 



