62 THE PLUMS OF NEW YORK. 



unless thinned the fruits are so small as to be hardly worth harvesting; 

 not infrequently trees die from over-bearing. A few varieties are un- 

 fruitful but usually because of defective pollination. Nearly all sucker 

 badly on their own roots, and except in cold regions should be grown on 

 other stocks. In general there are fewer pests to combat with these than 

 with the European plums but yet they are far from being exempt and 

 require on the grounds of this Station quite as much spraying as do other 

 plums. 



Waugh, who has given the subject much study, claims that the Amer- 

 icanas are not very strong sexually, 1 chiefly because of defective reproduc- 

 tive organs. He found in extensive examinations that 21.2 per ct. of 

 the pistils were defective, ranging from nothing in some varieties to 100 

 per ct. in others. More seldom the anthers were defective and the flowers 

 were sometimes proterandrous (the pollen maturing before the pistil is ready 

 to receive it), and that they were rather frequently proterogynous (the 

 pistils receptive before the pollen is mature). Waugh holds that in planting 

 these plums, provision should be made for cross-pollination, and recom- 

 mends as sorts most suitable for inter-planting for this purpose, other 

 varieties of the same species. 



Plant -breeders have not found that this species hybridizes as readily 

 as most of the other cultivated native plums. This is chiefly due to a 

 seeming lack of affinity for other species. Nevertheless there are numerous 

 Americana hybrids, and it is likely that as the high quality of the fruit 

 and the hardiness of the trees become better known they will be used 

 much more for hybridizing. 



The Americana plums are all hardy and some of the varieties can be 

 grown as far north as general agriculture is practiced. These, with the 

 Nigras, will probably always be the chief groups for dry, cold regions be- 

 tween the Great Lakes and the Rocky Mountains. They may also be re- 

 lied upon in the colder parts of New York and New England. The flower- 

 buds as well as the trees are hardy, having been known to withstand a 

 temperature of forty degrees below zero. Goff 2 reports that in the winter 

 of 1896-7 the flower-buds of Domestica varieties on the grounds of the 

 Wisconsin Experiment Station were almost totally destroyed though the 

 minimum temperature recorded was only twenty-three degrees below zero, 

 but the flower-buds of Americana varieties were not at all injured. Since 



'Waugh, F. A. Plum Cult. 51, 282-307. 1901. 

 'Goff, E. S. Wis. Sta. Bui. 63:4. 1897. 



