208 Plant-Breeding 



none the less so now that we have challenged its role 

 in the evolution of the plant kingdom. For the time 

 being, the new discussions of hybridizations are likely 

 to overshadow all other agencies in plant-breeding; but 

 selection under cultivation is as important now as it was 

 in the days of van Mons and Darwin. 



Conclusion. Now, in conclusion, what are ihe great 

 things that we have learned from these newer studies? 

 (1) In the first place, we have been brought to a full stop 

 in respect to our ways of thinking on these evolution 

 subjects. (2) We are compelled to give up forever the 

 taxonomic idea of rigid species as a basis for studying the 

 process of evolution. (3) The experimental method has 

 finally been completely launched and set under way. 

 Laboratory methods, comparative morphology, embry- 

 ological recapitulation, life-history studies, ecological in- 

 vestigations all these means are likely to be overshad- 

 owed for a time by experiments in actually growing the 

 things under conditions of control. (4) We must study 

 great numbers of individuals and employ statistical 

 methods of comparison. (5) The doctrine of discontin- 

 uous evolution is now clearly before us. (6) We are 

 beginning to find a pathway through the bewildering maze 

 of hybridization. 



