THE PLUMS OF NEW YORK. 15 



This hypothesis is based upon the supposition that when Domestica plums 

 run wild they revert to the Insititia or Spinosa form. It is not difficult 

 to test this theory. A study of the origin of the several hundred Domestica 

 and Insititia plums discussed in Chapters III and IV of The Plums of 

 New York does not show for any one of them a tendency to reversion or 

 evolution to other species; nor do the descriptions indicate that there 

 are many, if any, transitional forms. During the two thousand years 

 they have been cultivated in Europe the Old World plums have been 

 constant to type. Domestica seedlings vary somewhat but they do not 

 depart greatly from a well marked type. Such very few striking departures 

 as there seem to be are more likely to have arisen through crossing with 

 other species than through reversion or evolution. This Station has grown 

 many pure seedlings or crosses of varieties of Domestica within the species 

 and has had opportunity of examining many more from other parts of the 

 State, and none of these show reversion to the other two Old World species. 

 Nor, as we shall see, is there much in what is known of the history of these 

 three species to lead to the belief that the Domestica, Insititia and Spinosa 

 plums constitute but one wild species or have arisen from one. 



It has been remarked that there are few, if any, transitional forms 

 between the Domestica and other European plums. It is a significant 

 fact that Prunus domestica can be hybridized with other species of plums 

 only with comparative difficulty, species of plums as a rule hybridizing 

 very freely. This is as true with the Insititia and Spinosa as of other 

 plums, there being few recorded hybrids of either of these species with the 

 one under discussion. Quite to the contrary the varieties of the several 

 pomological groups of Domestica plums hybridize very freely. If all were 

 of one species we should expect many hybrids between the Domestica, 

 Insititia and Spinosa plums. 



We are now left with the third hypothesis, which is, as we have indi- 

 cated in a preceding paragraph, that the varieties of Domestica plums 

 belong to one species; or if they have come from more than one species 

 the wild forms have not been distinguished and must have grown under 

 much more nearly similar conditions than is the case with Prunus domes- 

 tica and any other species. Without knowledge of more than one wild 

 form, and in view of the intercrossing of the varieties of these plums it 

 seems best to consider all as parts of one species, leaving to the pomologist 

 the division of the species into horticultural groups founded on the char- 

 acters which make the fruit valuable for cultivation. 



