HYBRIDIZATION AND SELECTION. 



49 



The writer severed his connection with the Washington Agri- 

 cultural Experiment Station at the beginning of 1902, but his suc- 

 cessor and his assistants continued the work with the hybrid wheats, 

 and this work is still in progress, being conducted by Mr. C. W. 

 Lawrence, of the Washington station. 



Three of these hybrid varieties (which had been fixed by proper 

 selection, methods of which are outlined below) were distributed 

 in small quantities to the farmers in the fall of 1907. after having 

 been carefully tested at the experiment station as to their yielding 

 power. In the fall of 1908, 39,000 acres of these new varieties were 

 reported as being sown by the farmers in eastern Washington. In 

 two more years there will doubtless be seed enough for all. 



The case just cited illustrates one in which hybridization furnishes 

 a means of securing new and valuable varieties, namely, the case 

 where certain valuable characteristics are found in different varieties 

 and it is desirable to unite these characteristics. Such cases would 

 exist at most plant-breeding stations. Doctor Nilsson, at Svalof, 

 has made extended use of these principles in producing new varieties 

 of cereals at his station. The first task is to select the varieties 

 having desirable characteristics. Frequently some of the charac- 

 teristics will be found in varieties that are otherwise worthless, so 

 far as their use as field crops is concerned, so that in breeding work 

 a variety should not be rejected because of a single weakness. It is 

 legitimate to use an inferior variety in crossing, provided it has some 

 valuable characteristics. 



In working with self-fertilized crops the principles involved for 

 the first two years are exactly the same as those in cross-fertilized 

 crops illustrated in Table VI. The first generation of the hybrid 

 is heterozygote for all those characteristics in which the two parent 

 varieties differ. Where the parents differ in a great many respects 

 the problem becomes quite complex, for the number of types that 

 will be produced in the second generation is equal to 2 ^, n being the 

 number of points in which the two parents differ. Thus, when they 

 differ in one particular, that is, when we have one pair of allelomorphs 

 to deal with, there are two distinct types in the second generation 

 of the hybrid. If the parents differ in two respects, we have 2^=4 

 distinct types in ¥^ (the second generation of the hybrid). Three 

 differences give 2^=8 types, and so on. The figures given above 

 assume that in each pair of allelomorphs there is complete dominance, 

 so that the heterozygotes can not be distinguished from the pure 

 dominants. If the heterozygotes can be distinguished, then the 

 number of visibly different types in the second generation is 3"^. 

 In fact, in so far as their content of hereditary characters is con- 

 cerned there are always 3 types in the second generation when the 



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