LUTHER BURBANK 



also the pear and the apple, the pear and the 

 quince, and the quince and the apple; and yet 

 again, the petunia and the tobacco, and the crinum 

 and the amaryllis. But in each of these cases, 

 while very interesting hybrids were produced, 

 they were entirely sterile, and the experiment 

 could go no further. 



Sometimes species are crossed that are just 

 widely enough divergent so that the offspring are 

 relatively infecund but not actually sterile. Such 

 was the case with the cross between the Persian 

 and the California walnut, the offspring of which 

 is a tree of enormously rapid growth, but bearing 

 only a handful of nuts; whereas another walnut 

 cross, that between the American black walnut of 

 the East and the California black walnut, is enor- 

 mously prolific, bearing bushels of nuts where the 

 other hybrid bears only individual specimens. 



The celebrated cross between the plum and the 

 apricot furnished interesting illustrations of the 

 same thing. Most of the hybrids thus produced 

 bore imperfect flowers lacking petals or stamens 

 or pistils, as the case might be. It was only after 

 many efforts a specimen was produced that was 

 fertile, yet ultimately the race of hybrid plum- 

 cots was so developed that it now has many varie- 

 ties, some of them being excessively prolific. Yet 

 another instance of the way in which the barriers 

 between species may be broken down by persistent 

 effort (through ultimately finding plants having 

 just the right degree of affinity) is that in which 

 Mr. Burbank produced the sunberry by crossing 



[30] 



