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251 



These two series may be expressed in terms of percentage by multiplying 

 each series by a factor that will change the value of the middle class to 

 100. The mean weight of all the mother beans was very nearly 50 eg. 

 while that of the progeny is approximately 40 eg. Thus the first series 

 is multiplied by 2 and the second by 2.5 giving the following result. 



Now the deviation of each progeny class can be compared directly with 

 the deviation of the mother class. 



Thus the ratios of the minus deviations of the progeny classes to the 

 minus deviations of the mother classes are %o an< ^ %<)> the mean of which 

 is I %Q or 0.163. Similarly for the plus deviations, %o> 1 Mo> l %o X ^3, 

 0.303. The average of these two values is 0.233 which is about y as 

 compared with Galton's observation of % inheritance in size of seed in 

 the sweet pea and stature in man. 



During these preliminary experiments, however, Johannsen noticed 

 that plants grown from similar sized beans produced beans of very differ- 

 ent sizes. Thus, for example, the plants grown from the largest mother 

 beans (about 80 eg. in weight) yielded seeds of strikingly different sizes. 

 The average weight of the seeds of these individual plants varied between 

 35 and 60 eg. and when the weights of all the individual beans of this 

 series were arranged in a frequency distribution it produced a series that 

 differed considerably from the normal frequency distribution. The 

 distribution of 598 seeds, all progeny of beans about 80 eg. in weight, 

 when arranged in classes of 5-cg. intervals, was as follows : 



Classes 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 



Number of seeds 5 1846144127 70 70632815 8 4 



Theoretical numbers 1 3 11 26 53 85 109 112 91 59 30 13 4 1 



M = 45.44 0.43 eg.; <r = 10.40 eg. 



Clearly this distribution if plotted would produce a skew polygon with the 

 mode to the left of the theoretical mode. This observation caused 

 Johannsen to have serious doubt regarding the biological justification of 

 Galton's law. For such a distribution did not appear to be the expression 

 of only one "type"; on the contrary, it seemed more likely that the 

 material was mixed. 



