Theories of Evolution 17 



mentary species are far more rare, but I have 

 discovered in the great evening-primrose, or 

 Oenothera lamarckiana a strain wMch is pro- 

 ducing them yearly in the wild state as well as 

 in my garden. These observations and pedi- 

 gree-experiments will be dealt with at due 

 length in subsequent lectures. 



Having proved the existence and importance 

 of mutations, it remains to inquire how far the 

 improvements may go which are due only to 

 fluctuating variability. As the term indicates, 

 this variability is fluctuating to and fro, oscil- 

 lating around an average type. It never fails 

 nor does it, under ordinary circumstances, de- 

 part far from the fixed average. 



But the deviation may be enlarged by a choice 

 of extremes. In sowing their seed, the aver- 

 age of the strain is seen to be changed, and in 

 repeating the experiment the change may be 

 considerable. It is not clear, whether theo- 

 retically by such an accumulation, deviations 

 might be reached which could not be attained at 

 once in a single sowing. This question is hard- 

 ly susceptible of an experimental answer, as it 

 would require such an enormous amount of seed 

 from a few mother plants as can scarcely ever 

 be produced. 



The whole character of the fluctuations shows 

 them to be of an opposite nature, contrasting 



