NILSSON'S DISCOVERY 43 



the title of the address deHvered by him in London in 1862, 

 in whicli he first pubHshcd liis results and his views. It 

 was entitled, "On pedigree in wheat as a means of increas- 

 ing crop." The improvement was obtained by the increase of 

 the size of the ears, their number of kernels and the size of 

 the latter. The number of heads on a plant he did not con- 

 sider as a subject of selection, but rather assumed that it was 

 wholly determined by the relative distance between the plants 

 and therefore by the space given them in sowing. For him, 

 the productiveness of a field was proportional to the yield 

 of the single ears. 



Moreover, he assumed that his pedigree-races were not 

 only to be ameliorated but must be kept up to their highest 

 point of development by continued selection. As soon as 

 selection ceased, they would return to their original starting 

 point and their superiority over the ordinary cultivated 

 varieties would disappear. This assertion has a distinct 

 and deep significance in agricultural practice, and has 

 gained a great deal of influence in the discussion of theoret- 

 ical questions as well. For practice it means that all the 

 seed destined for sowing should be produced directly from 

 the pedigree-stock, and that this is to be kept constantly 

 under the same conditions of treatment and sharp selection. 

 The truth of this assertion has been accepted by his custo- 

 mers, and this fact has left the production of seed grain 

 almost entirely in his hands. It is easy to see that the gain 

 made by the breeder of a new variety depends, for a large 

 part, on the acceptance of this proposition. In the varieties 

 produced by Lc Couteur and Shirreff, all seed is of equal 

 value, provided the races are kept pure and free from admix- 

 ture. Any" one may multiply them with the same success 

 as the original breeder, but on Hallett's principle all the 

 profit of the production of reUable seed grain was given into 

 the hands of him who kept the original pedigree. 



