Periodic Mutations 693 



natively mutating and constant species. Some 

 lines may be mutating at the present moment; 

 others may momentarily be constant. The mu- 

 tating lines will probably sooner or later revert 

 to the inactive state, while the powers of de- 

 velopment now dormant may then become awak- 

 ened on other branches. 



The view of permanency represents life as 

 being surrounded with unavoidable death, the 

 principle of periodicity, on the contrary, fol- 

 lows the idea of resurrection, granting the 

 possibility of future progression for all living 

 beings. At the same time it yields a more hope- 

 ful prospect for experimental inquiry. 



Experience must decide between the two main 

 theories. It demonstrates the existence of poly- 

 morphous genera, such as Draba and Viola and 

 hundreds of others. They clearly indicate a 

 previous state of mutability. Their systematic 

 relation is exactly what would be expected, if 

 they were the result of such a period. Perhaps 

 mutability has not wholly ceased in them, but 

 might be found to survive in some of their mem- 

 bers. Such very rich genera however, are not 

 the rule, but are exceptional cases, indicating 

 the rarity of powerful mutative changes. 



On the other hand, species may remain in a 

 state of constancy during long, apparently dur- 

 ing indefinite, ages. 



