LUTHER BURBANK 



Among all the thousands of types of prunes 

 grown on the seedlings of my hybrid colony or 

 on grafts on some receptive tree, there will be 

 individual fruits varying, let us say, from one- 

 half inch in length to perhaps two and a half 

 inches — but by no chance will there be a fruit 

 four inches in length. 



Similarly among my seedlings there will be 

 some that ripen their fruit as early as the first of 

 August, but none that ripen so early as the first 

 of July. 



Fruits of other species may ripen far earlier; 

 the cherry does so habitually. But the ancestors 

 of the plum have lived under conditions that made 

 it unnecessary for them to mature their fruit much 

 before midsummer. So their range of habit in 

 this regard, as recorded in the stored hereditary 

 tendencies, was strictly limited. And the possi- 

 bilities of variation among my hybrid seedlings 

 are correspondingly limited, because, as I have 

 hitherto pointed out, heredity is but the symbol of 

 the sum of past environments, and the hereditary 

 limitations of any common race of plants to-day 

 are determined by the aggregate limitations of all 

 their ancestors. 



Reversion to the Average 



Such an analysis, in which the varying con- 

 ditions that environ the different strains of a 



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