THEORIES OF DEVELOPMENT 



two species of solaimm, that he had attempted 

 ineffectually to cross from time to time for 

 twenty-five years, success finally coming in the 

 form of a single fertile seed case. 



MENDELIAN HEEEDITY 



(4) As to later progress of hybrid races. 

 Whereas sometimes, in case of the Primus berry, 

 a hybrid shows a combination of the traits of the 

 parents, constituting a new type that breeds true, 

 this is not the usual result of crossing different 

 species or marked varieties. As a rule, the hybrid 

 shows a tendency, as regards any given character, 

 to follow one parent to the exclusion of the other. 

 If, for example, you can cross a stoneless plum 

 with an ordinary plum, you must expect that all 

 the progeny will bear stone fruit. 



But Mr. Burbank early made the discovery that 

 if hybrid forms are allowed to interbreed, their 

 progeny usually show an extraordinary tendency 

 to variation, some of them reverting in one direc- 

 tion and some in another, and some individuals 

 combining the traits of the two divergent lines 

 of ancestry in new combinations. He discovered 

 that the best opportunity was afforded for the 

 development of new types ; and he eagerly put this 

 discovery to account in numberless breeding ex- 

 periments. 



Now this discovery, made by Mr. Burbank in 

 the early eighties, is essentially the discovery that 

 had been made twenty years before by Gregor 



[31] 



