252 



GENETICS IN RELATION TO AGRICULTURE 



This state of affairs was the starting point of further critical study. 

 In order to take account of the effect of selection supposedly in the 

 opposite direction, he next examined the progeny of the smallest mother 

 beans (about 30 eg.) and found that they displayed no such striking 

 irregularity as did the progeny of the largest beans. (Possibly this was 

 due to the fact that about 20 plants were grown from the smallest beans 

 while the progeny of the largest beans came from only 11 plants.) The 

 progeny seeds from the smallest mother beans were weighed individually 

 and the data put in the form of a frequency table as in the former case. 



Classes 15 20 25 30 35 40 45 50 55 60 65 



Number of seeds 8 18 71 156 172 127 35 15 3 6 



Theoretical numbers 1 6 27 77 139 162 121 57 17 3 1 



M = 36.68 0.30 eg. ; a- = 7.33 eg. 



This distribution does not indicate a mixture. Instead it suggests that a 

 single original "weight type" of bean was set apart by selection in the 

 minus direction. The general result of this preliminary study was cer- 

 tainly a sort of confirmation of Galtonian regression ; but at the same time 

 the doubt was aroused whether the original population was not a hetero- 

 geneous mixture from which selection simply sorted out already existing 

 "types". Hence came the question: Will selection of plus or minus 

 variants within pure lines bring about the isolation of types and cause 

 Galtonian regression? 



This question was answered the following year (1902). A series of 

 19 pure lines was used for this investigation. Each of these pure lines 

 originated from a single bean from the crop of 1900. In the fall of 1901 

 each line was represented by the seeds of one plant. In 1902 he planted 

 524 seeds. Every seed was given a number and each plant was harvested 

 separately. Each pure line, each plant and every single bean was sepa- 

 rately numbered. Thus each individual could be compared with every 

 other individual. Johannsen first compared his material as a whole with 

 the results of his preliminary study. Having recorded the weight of 

 each bean, he arranged the data in groups corresponding to the classes 

 of mother beans as in the previous year. 



Again he found about 34 inheritance and % regression of progeny on 

 mother beans. He next divided each of these six groups of progeny 

 beans into classes according to weight as shown in Table XL. 



