84 Otitline of Genetics 



The question arises whether there is any way of avoiding this 

 impossible situation. The escape is suggested by the fact that 

 time can take the place of numbers. East has shown that by 

 growing looo individuals in the F2 generation, 100 in the F3, and 

 50 in the F4, one stands as much chance of getting the desired 

 combination as by growing 250,000 in the F2, provided an intelli- 

 gent selection is made in each generation. In other words, one 

 who understands the mechanism of the inheritance of quantita- 

 tive characters will grow only 1000 individuals in the F2 genera- 

 tion, and will select for seed only those individuals with the most 

 favorable combination of factors. In this way, by intelligent 

 selection, factors are 'Spiled up" in the right direction from year 

 to year. In a few years the desired result will be reached without 

 the necessity of ever growing a very large number of individuals. 

 Such work is practicable at experiment stations, and it is the kind 

 of work that a number of them have been doing. Even the farmer 

 is able to accomplish this. Although his selection of individuals 

 is not quite as intelligent as that of a scientific breeder, he is at 

 least selecting in the right direction and making some advance. 

 A little more time and a little more acreage would bring him very 

 close to the desired goal. 



A further application of the cumulative factor hypothesis 

 may be considered. The practice we have been discussing under 

 the title of "inheritance of quantitative characters" seems to be 

 little more than what has already been called artificial selection, 

 which is the oldest of all methods of plant breeding. It is a method 

 that was thought to be discredited entirely by the work of De Vries 

 and JoHANNSEN when they discovered ''elementary species" or 

 ''pure lines," and demonstrated that artificial selection could never 

 result in any large or permanent improvement. In consequence 

 of this, artificial selection, as the most important method of secur- 

 ing desirable races, gave place to pedigree culture at a number of 

 experiment stations. The older method was not entirely aban- 

 doned, for it had its uses, but many regarded it as a medieval 

 method of breeding. The artificial selection which we have been 

 describing, however, is distinctly different from the method prac- 

 ticed by the early breeders. In brief statement, the difference is 

 as follows. 



