214 



EVOLUTION, GENETICS, AND EUGENICS 



Pure Line I. The snape of the curve, the mode, and average size were 

 different. Again selection for six generations of, first, the largest beans 

 for seed, and second, the smallest beans for seed, did not affect the 

 variation curve, mode, or average. Once again, selection within a 

 pure line was quite ineffective. 



The same results were obtained in all the rest of the nineteen orig- 

 inal pure lines with which Johannsen experimented. 



A somewhat more concrete idea of the results obtained may be 

 secured through the perusal of the following table which gives in terms 



RESULTS OF SELECTION IN PURE LINE I 



Harvest Year 



1902 



I903 

 1904 



I905 

 1906 

 1907 



Mean Weight of Selected 

 Parent Seed 



Minus 



60 



55 

 50 



43 

 46 



56 



Plus 



70 

 80 



87 



73 

 84 



Si 



Mean Weight of 

 Offspring 



From Minus 

 Parent 



75 



54 

 63 

 74 

 69 



15 

 19 



59 

 55 

 38 

 07 



From Plus 

 Parent 



64.85 

 70.88 

 56.68 

 63.64 

 73.OO 

 67.66 



of average bean weight the results of selecting plus and minus parents 

 for six generations in Pure Line I, the plus parents being largest beans 

 and minus parents being smallest beans. 



It will be seen that in the last year of this selection experiment 

 (1907) the smallest beans, averaging 56 eg. in weight, produced a prog- 

 eny weighing, on the average, 69.07 eg., while the largest beans of the 

 same year, averaging 81 eg., produced progeny of practically the same 

 average weight as did the smallest beans, namely, 67.66 eg. The dif- 

 ference is not statistically significant. The influence of the environ- 

 ment in bean weight is clearly shown in the data for the year 1904, 

 which was a bad year for growth. In this year, the average weight of 

 progeny from both large and small beans was greatly reduced, being 

 respectively 56.68 eg. and 54.59 eg. That this loss in weight was not 

 inherited is shown by the results in subsequent years in which the 

 average returned to that seen in the first year of selection. It is also 

 interesting to note that in the years 1903, 1906, and 1907 the lighter 

 parents produced a heavier progeny than did the heavier parents. 



From these experiments Johannsen came to the conclusion that 

 plus and minus fluctuations about the mode were due to differences in 



