518 



ANNUAL KEPORT SMITHSONIAN INSTITUTION, 1908. 



elected for survival and others doomed to destruction no matter how 

 numerously or how long they may be thrown off by the parental type. 

 As to the periodicity of mutations our information is not very 

 extensive. Does a species, as it produces generation after generation 

 in the course of centuries, arrive at a point where it begins to give 

 off atjpic individuals, and is this process continued for a time and 

 then discontinued? We can only say that we find some species 

 mutating and others not ; we have not seen either the opening or clos- 

 ing of the mutative period in any species. This consideration is com- 



Fig. 5. — Correlation table of length and width of leaf in 0. ruhrinervis. (p=0.6604± 



0.0119.) (After Shull.) 



plicated, however, with that of the frequency of the mutants. Thus 

 in Lamarck's evening primrose five in every hundred plants are mu- 

 tants, and it is conceivable that the atypic form might not occur more 

 than once in a thousand, or once in ten thousand, or once in a million. 

 These large numbers of plants of any species are not all in existence 

 at any one time, and it might take years, or even decades, to bring 

 one mutant within the range of the possible number, in which case 

 a false conception of the mutative period might be gained. It is 

 suggested, therefore, that the conception of frequency of mutation is 



