78 LUTHER BURBANK 



same branches, are giants that surpass even their 

 hybrid parent, not to mention their moderate- 

 sized grandparents? The fact of this diversity is 

 unquestionable. It affords a surprise to all who 

 inspect the trees of this strangely diversified 

 fraternity. 



But how explain it? 



A clue to the explanation is gained when we 

 learn that a California walnut, which, it will be 

 recalled, was a parent form in each of the hybrid 

 strains, is a tree showing great variability in the 

 matter of size when growing in a state of nature. 

 In the northern and central parts of California 

 it is usually a large spreading tree, often with 

 gracefully drooping limbs. But farther to the 

 south it becomes a mere shrub, and on the moun- 

 tains and hills about Los Angeles it is only a 

 bush. The nut diminishes in size correspondingly 

 until, in Texas and Mexico, it is scarcely larger 

 than a pea. 



When growing still farther to the south, in 

 New Mexico and Texas, the black walnut is 

 sometimes classified as a different species. 



It appears to me, however, that these dwarfed 

 southern forms are only varieties that have ac- 

 quired different characteristics through the in- 

 fluence of what for them has proved an unfavor- 

 able environment. In any event there is no 



