82 LUTHER BURBANK 



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 de- 

 velopment of these new races of giants. 



As yet we are not denied at least a hypotheti- 

 cal 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 wal- 

 nuts 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 Cretaceous Age. 



In that time, as the records in the rocks 

 abundantly prove, the conditions of climate now 

 restricted to the tropics prevailed even in the 

 temperate zones, and the vegetable life was char- 



