430 PRACTICAL BOTANY 



394. Results of hybridizing small fruits. The most familiar 

 hybrids among small fruits are grapes. It is probable that the 

 Delaware and the Catawba are hybrids, and the Salem, Brigh- 

 ton, and Diamond certainly are. Many varieties are directly or 

 remotely descended from hybrids between the European wine 

 grape and our northern fox grape, two wholly distinct species. 



d 

 FIG. 341. Hybrid plums 



a, a stoneless wild plum ; b, c, d, fruit of hybrids of a with the French prune plum 

 All drawn to the same scale 



A favorite blackberry, the Wilson Early, is a hybrid between 

 two common wild species, the high blackberry 1 and the dew- 

 berry. 2 Among the descendants of hybrids between an almost 

 inedible species 3 from Siberia and an edible one 4 from Cali- 

 fornia is a new constant species (not a variety), the Primus 

 blackberry. 



Hybrid plums in the greatest variety have been produced 

 by plant breeders, especially by the well-known grower of 

 horticultural novelties, Luther Burbank. The amount of vari- 

 ation in the offspring of a single hybrid is suggested by 

 Fig. 341. One fruit of great value, the Climax plum, was 

 bred by Burbank as a hybrid between a bitter, tomato-shaped 

 Chinese plum and a Japanese plum. 



395. Results of hybridizing citrous fruits. Most valuable 

 and interesting work in hybridizing plants of the Orange fam- 

 ily has been done by the United States Department of Agri- 

 culture, under the direction of Dr. H. J. Webber. 5 The hardy 



1 Rubus allegheniensis. 3 R. cratcegifolius. 



2 R. villosus. 4 R. vitifolius. 



6 See Yearbook of the Department of Agriculture, 1904. 



