474 Plant Physiology 



sions were primarily the result of extensive studies upon 

 the evening primrose ((Enothera Lamarckiana) , and upon 

 a general review of available information respecting both 

 the origin of domesticated varieties, and the behavior of 

 organisms in nature. Even though some hesitate to 

 accept all the conclusions arrived at for the (Enothera 

 mutants, the principle of mutation has been accepted by 

 many students of evolution as a working hypothesis ; 

 and many are now endeavoring to determine the extent, 

 frequency, and behavior of such mutants. 



According to the current view a mutation may be a 

 variation relatively great or small, involving a single unit 

 character or a group of such characters. The mutation 

 is often of greater, but may be of lesser, extent than the 

 fluctuation, and the existence of the two types together 

 may lead to much confusion. Far more careful analytical 

 work will be required before it may be possible fairly to 

 estimate the respective value in evolution of mutation and 

 fluctuation, or indeed properly to distinguish types of 

 variation. There can be no doubt that striking cases 

 are on record of the occurrence of saltation ; but it is 

 obvious that the extreme supporters of the mutation 

 principle, by the definition and explanation of the term, 

 actually exclude the possibility of any such phenomenon 

 as transmissible fluctuation. 



Tower and Blaringhem working with beetles and with 

 corn respectively have reported some results particularly 

 interesting in this connection. After demonstrating the 

 effect of environment in producing continuous variation 

 in Chrysomelid beetles within the range of the species, 

 Tower reports a striking case of difference in behavior. 



