320 ESSENTIALS OF BOTANY 
A favorite blackberry, the Wilson Early, is a hybrid be- 
tween two common wild species, the high blackberry ? and 
Fig. 224. 
A, the tangelo, a hybrid between the tan- 
gerine and the grape-fruit; B, the grape- 
fruit (one parent of .A). 
the dewberry.2, Among 
the descendants of hy- 
brids between an almost 
uneatable species * from 
Siberia and an eatable 
species * from California 
is a new constant spe- 
cies (not a variety), the 
Primus blackberry. 
Hybrid plums in the 
greatest variety have 
been produced by plant 
breeders, especially by 
the well-known Cali- 
fornian experimenter, 
Luther Burbank. The 
amount of variation in 
the offspring of a single 
hybrid is well shown by 
Fig. 223. One fruit of 
great value, the Climax 
plum, was bred by this 
experimenter as a hybrid 
between a bitter, tomato- 
shaped Chinese plum 
and a Japanese plum. 
400. Results of Hybridizing Citrous Fruits.— Most valua- 
ble and interesting work in hybridizing plants of the Orange 
family has been done by the United States Department of 
1 Rubus villosus. 2 R.canadensis. *% R.crutegifolius. * R. vitifolius. 
