22 MUTATIONS, VARIATIONS, AND RELATIONSHIPS OF THE OENOTHERAS. 



part of the plan for the present study that this comparison should be contin- 

 ued, but unfortunately the seed of 0. nanella gave only 3 germinations and 

 the continuation of this comparison must be postponed until another season, 

 but meanwhile it will be particularly interesting to make another comparison 

 of heights which will present something of a contrast with that between O. 

 nanella and its parent. It will be recalled that in that comparison the co- 

 existence of two striking features was taken to be more than a mere coinci- 

 dence, namely, the great departure of the mean value in O. nanella from the 



30 1 



5 



ao 



15 



10 



66-70 71-75 76-80 81-85 86-90 91-95 96-100 101-105 106-110 111-115 116-120 



FIG. 2. Comparison of the variability of stem-heights of Oenothera lamarckiana (broken curve) 

 and O. riihruic-rris, as grown at the Station for Experimental Evolution in 1905. 



mean of its parent, and a very great increase in the coefficient of variability 

 in the heights of the mutant. In comparing the heights of 0. i-nhriucrris with 

 those of 0. lamarckiana there is seen a very much less marked departure from 

 the parental condition in the mean values, and a correspondingly slight 

 increase in the coefficient of variability. This comparison is shown graphic- 

 ally in fig. 2 and is expressed numerically as follows: 



Variation in heights, 1905. 



This may still be merely a coincidence, but two such coincidences are very 

 much less likely to occur than one, and the attempt will be made in the study 

 of other characters to trace the suggested parallel between the departure of 

 the mean from the parental condition and the increase in the value of the 

 coefficient of variability. 



