120 PROCEEDINGS OF THE OHIO ACADEMY OF SCIENCE 



gations were also made (Fischer, MacDougal, Tower, etc.) 

 where organisms were subjected to stimuli abnormal in 

 their nature with the result that a modified progeny was 

 obtained which bred true to the apparently induced char- 

 acter in succeeding generations. Furthermore, cytological 

 studies (Gates, etc.) demonstrated some interesting rela- 

 tionships so far as differences in chromosome composition 

 among "mutants" were concerned. 



While the evidence is far too insufficient to allow more 

 than a tentative opinion, there are several conclusions con- 

 cerning mutation which appear justified. The nature of 

 the results obtained through the various agencies makes it 

 quite evident that they are not all due to a single underlying 

 principle. There are many "mutants" the origin of which is 

 most certainly to be explained on the basis of a hetero- 

 zygous condition of the gametes, and much evidence has 

 accumulated that O. lamarckiana of Devries, on which the 

 mutation theory was founded, belongs to this class. Fur- 

 thermore, there are mutants developing in connection with 

 the action of abnormal stimuli, although it is not at all im- 

 probable that some of these result from heterozygotes. It 

 may be mentioned that Humbert (1911) in experiments 

 with 7500 pure line plants of Silene noctiflora, one of the 

 "pinks," utilizing methods similar to those of MacDougal, 

 failed to obtain any "mutants." Another explanation of the 

 results in connection with the influence of abnormal stim- 

 uli is that the modification takes place through the destruc- 

 tion of a factor and thus the process is one of subtraction 

 instead of addition. There are also investigations, notably 

 those of Gates, in which the aberrant organism apparently 

 results from the abnormal behavior of the chromosomes 

 at some stage during the life cycle. Oenothera gigas with 

 its tetraploid chromosomes is here of much interest. 



Notwithstanding these diverse results, there is little 

 indication that anything actually new has been added to the 

 organism which would not have occurred within a pure line. 

 If this is true the heterogeneous school of mutationists can 



