Hypothesis of Mutations 707 



mutations at sufficient length on a previous oc- 

 casion. Only the instance of the peloric toad- 

 flax might be recalled here, because the historic 

 and geographic evidence, combined with the re- 

 sult of our pedigree-experiment, plainly shows 

 that peloric mutations are quite independent of 

 any periodic condition. They may occur any- 

 where in the wide range of the toad-flax, and the 

 capacity o^ repeatedly producing them has 

 lasted some centuries at least, and is perhaps 

 even as old as the species itself. 



Leaving aside such stray mutations, we may 

 now consider the probable constitution of the 

 great lines of the genealogic tree of the evening- 

 primroses, and of the whole vegetable and ani- 

 mal kingdom at large. The idea of drawing up 

 a pedigree for the chief groups of living organ- 

 isms is originally due to Haeckel, who used this 

 graphic method to support the Darwinian the- 

 ory of descent. Of course, Haeckel 's genealogic 

 trees are of a purely hypothetic nature, and have 

 no other purpose than to convey a clear concep- 

 tion of the notion of descent, and of the great 

 lines of evolution at large. Obviously all de- 

 tails are subject to doubt, and many have ac- 

 cordingly been changed by his successors. These 

 changes may be considered as partial improve- 

 ments, and the somewhat picturesque form of 

 Haeckel 's pedigree might well be replaced by 



