220 THE EVOLUTION OF OUR NATIVE FRUITS 



what different stone ; but all of these characters are 

 eminently variable in plums, and they seem, for the 

 most part, to be the result of adaptation to habitat. 

 We shall recur to this sand plum in our discussion 

 of the Utah Hybrid Cherry (page 244.) 



The latest contribution to our knowledge of the 

 sand plums is the following sketch by Waugh : * 



Although it is now nearly four years since Sargent distin- 

 guished Pnotu.s Watsoni from P. angustifolia (C. S. Sargent, 

 Garden and Forest, vol. vii., p. 134, 189-4), the individuality of 

 the group does not seem to have made any very decided impres- 

 sion either upon botanists or horticulturists, and material which 

 ought to be referred to this species is still sometimes carelessly 

 classified with the Chickasaw plums. As the group has already 

 given some evidence of utility, and as it may prove of consider- 

 ably greater importance in the future evolution of American 

 plums, it appears to be especially desirable to have the knowl- 

 edge of it clearly in the minds of plum students. 



The most striking difference between the sand plum and the 

 Chickasaw is that of stature. The sand plum is distinctly a 

 dwarf, seldom growing much higher than a man's head, and sonic- 

 times reaching maturity and prolific fruitage at a height of four 

 feet. Beside this, the whole dwarfish appearance is measurably 

 intensified by the short-jointed, often sharply-zigzagging twigs, 

 which give an effect of thorniness. These twigs are apt to be 

 ashy-e;ray, especially at two or three years of age. The leaves are 

 smaller than those of the Chickasaw plums, and are more finely 



erenulate upon the margins, but offer no sate distinctive char- 

 acters. In the most carefully prepared published descriptions of 

 the two species, the few distinctions given are hard to apply. Of 

 Prunus angustifolia the calyx lobes are said to be glandular- filiate, 

 while those of /'. Watsoni are described as eglandular-ciliate. 

 And while all the garden and herbarium specimens of /'. Watsoni 



which 1 have examined have shown eglandular calyx lolx ■-. so 



have several of the cultivated varieties of Chickasaw parentage. 



The two species are evidently closely related, hut one who is 



*"Thc Sand Plums," ('mint i \ Gentleman, January 27, 1898. 



