78 MUTATIONS, VARIATIONS, AND RELATIONSHIPS OF THE OENOTHERAS. 



tions were induced, although vague statements and erroneous generalizations 

 to the contrary are current. The possibility of such results is to be by no 

 means denied, but if this view is to be upheld it must be supported by some 

 evidence based upon actual experimentation. Vicinism, the somatic multipli- 

 cation of bud-sports and extreme variants, and the confusion of closely related 

 elementary species form the basis for the greater number of positive assertions 

 as to the effects of cultivation, and it is necessary to examine all facts bearing 

 upon the lineage of supposedly new forms with the greatest care before their 

 aspect or behavior may be taken as evidence upon phylogenetic problems. 



An extended consideration of the phenomena of mutability has led the 

 authors of this paper to entertain grave doubts as to the practical value of 

 the conception of periodicity. De Vries throughout his writings has favored 

 the assumption, on purely theoretical grounds, that a species must, at certain 

 times in its history, be in a mutable condition, while in other periods of great 

 length all of the progeny come true to the type, subject only to fluctuating 

 variability. 



It is quite possible that any given form may give off derivatives steadily 

 for centuries, but none of these being fitted to survive, no trace of this activity 

 remains. A change in the character of the mutants originated, or newly 

 found conditions met with in comparatively short migrations, might readily 

 give an appearance of the beginning of a mutative period, unless the matter 

 had been tested by pedigree-cultures. 



With regard to the actual succession of generations two aspects of the case 

 present themselves. In one case it may be supposed that an annual species 

 might have a limited distribution, and, occupying small areas, might be repre- 

 sented by only a few individuals every year. Combined with these circum- 

 stances, the proportion of mutants produced by the species might be so small 

 that it would be possible to examine every specimen for a hundred years 

 without meeting a single atypic individual. The conclusion would then be 

 reached that this was included in the immutable period. Then if the number 

 of individuals grown and examined in the next ten years numbered as many 

 millions, and some mutants were found, the line of reasoning followed would 

 lead to the fallacious assumption that a mutable period had begun, or rather 

 that some physiological change had ensued in consequence of which mutations 

 were occurring. These might as readily be seen during the first year of 

 observation, however, if enough individuals had been grown. 



It appears, therefore, that the real state of affairs is better represented by 

 the phrase "frequency of mutation," by which is expressed the number of 

 individuals which must be grown to furnish one mutant, and which is nearly 

 identical with "the coefficient" of mutability. If the parental type pro- 

 duces more than one mutant, the frequency of these may vary widely from 

 each other. 



