CONTINUOUS SELECTION 411 



effected in recent times. In the first place much care and 

 thought have been devoted to carrying out experiments in 

 accordance with the principle of continuous selection : 



" The general custom [in Germany] was to start such experi- 

 ments from the best local or improved varieties by an initial choice 

 of a certain number of typical heads. Such a group of selected 

 plants was called the elite, and this elite had to be ameliorated 

 according to the prevailing demands or even simply in accordance 

 with some ideal model. Year after year, the best ears of the 

 elite group were chosen for the continuance of the strain or 

 family, and slowly, but gradually, its qualities were seen to 

 improve in the desired direction. After some years, such a 

 family might become decidedly better than the variety from 

 which it had been derived. Then its yearly harvest would be 

 divided into two parts, after having been sufficiently purified by 

 the rejection of accidental ears of minor worth. The best ears 

 were carefully sought out and laid aside for the continuance of 

 the elite strain, but the remainder were sown on a distant field 

 in order to be multiplied as fast as possible. By this means, after 

 a multiplication during two or three generations, its product 

 could be used as seed grain for the farm or sold to others for 

 the same purpose. Each year the elite would, of course, give a 

 new and better harvest which could be multiplied and sold in the 

 same manner." 1 



By this method improvement may undoubtedly be effected, 

 but the selection has to be constantly repeated, otherwise the 

 improved strain rapidly deteriorates again. Indeed it may be 

 questioned whether it is possible in this way to effect any per- 

 manent improvement, at any rate in the case of cereals. One 

 reason for this appears to be that we are dealing all the time, 

 not with a single pure race, but with a mixture of distinct races. 

 We must also remember that many of the characters which it is 

 desired to perpetuate and increase may be the direct result of the 

 cultural methods employed, and, as we have already seen, we 

 cannot expect such causes to produce visibly heritable effects in 

 the course of a few generations, whatever they might do in the 

 long run. 



We have had occasion to point out in an earlier chapter that, 

 according to Professor de Vries, new species arise, in a state of 

 nature, not by the accumulation in particular directions of small, 

 fluctuating variations, but by the sudden appearance of those 



1 De Vries, op. cit., p. 58. 



