500 Mutations 



converted into rays. This conversion is ob- 

 viously the true mark of the doubling, and be- 

 fore traces of it are found no assertion whatever 

 can be given as to the issue of the pedigree-ex- 

 periment. 



Three more years were required before this 

 first but decisive trace was discovered. During 

 these years I subjected my strain to the same 

 sharp selection as has already been described. 

 The chosen ancestor of the race had flowered in 

 1896, and the next year I sowed its seeds only. 

 From this generation I chose the one plant with 

 the largest number of rays in its terminal head, 

 and repeated this in the following year. 



The consequence was that the average num- 

 ber of rays increased rapidly, and with it the 

 absolute maximum of the whole strain. The 

 average came up from 21 to 34. Brighter and 

 brighter crowns of the yellow rays improved 

 my race, until it became difficult and very time- 

 consuming to count all the large rays of the bor- 

 ders. The largest numbers determined in the 

 succeeding generations increased by leaps from 

 21 to 34 in the first year, and thence to 48 and 66 

 in the two succeeding summers. Every year I 

 was able to save enough seed from the very best 

 plant and to use it only for the continuance of 

 the race. Before the selected plants were al- 

 lowed to open the flowers from which the seed 



