LUTHER BURBANK 



their parents? So far as we are aware, there is 

 no record of a pure bred walnut of any of the 

 three species involved that ever showed such 

 capacity for rapid growth or such propensity to 

 continue growing until it attains colossal propor- 

 tions as the hybrids manifest. 



There is no recorded or observed ancestor 

 to whom we can appeal in explanation of the 

 development of these new races of giants. 



As yet we are not denied at least a hypothetical 

 explanation that may perhaps account for the 

 observed colossal growth of these new races of 

 trees. The explanation demands that we go back 

 in imagination through very long periods of time, 

 and consider the ancestors of our walnuts not 

 merely for hundreds of generations but for 

 thousands or perhaps for millions of generations. 



It is necessary, in short, to trace backward the 

 ancestral history of the walnut to those remote 

 epochs when the primordial strain from which 

 the present trees have developed grew in tropical 

 regions, and, in common with tropical vegetation 

 in general, doubtless acquired the habit of luxu- 

 riant development. 



It is permissible even that we should place in 

 evidence the exuberant vegetation of that remote 

 geological era known as the Carboniferous Age. 



In that time, as the records in the rocks 



[162] 



