THE SCENTED CALLA 



form suddenly assumed. Professor de Vries spoke 

 of these sudden and wide variations from type on 

 the part of his evening primrose as constituting 

 "mutations." 



He conceived the idea that similar mutations 

 or sudden wide variations had probably consti- 

 tuted the material on which natural selection 

 had worked in the past. Such mutations being 

 observed to occur in the case of the evening 

 primrose, it is not unnatural to argue that 

 similar mutations must occur in the case of other 

 organisms; and it requires no argument to show 

 that such wide variations offer better material for 

 the operation of the laws of natural selection than 

 could be offered by the minute and inconspicuous 

 variations that had hitherto been supposed to 

 constitute the basis of evolutionary changes. 



There were many reasons why the mutation 

 theory appealed to contemporary biologists, thus 

 accounting for its very cordial reception. 



For example, there are numberless instances 

 in nature where the development of a useful 

 organ is exceedingly hard to explain on the basis 

 of natural selection, because the organ in its 

 incipient stages could have no utility. Similarly 

 a modification in the location of an organ — say 

 the shift in the flatfish's eye until both eyes are on 

 one side — ^is difficult to explain as a process taking 



[91]' 



