CHAPTER X 



THE PROBLEMS OF THE PRACTICAL BREEDER 



THE applications of theory to the work of practical 

 breeding have been indicated here and there, but it 

 may be well to discuss the subject somewhat more 

 systematically. 



PLANT BREEDING 



Considering first the applications of Mendelism in 

 plant breeding, it will be clear that Mendel's law points 

 out an easy method by which definite characters from 

 two existing varieties may be recombined in one. Much 

 valuable work has been done in the past in this direc- 

 tion, but it has often been accomplished at the expense 

 of a good deal of unnecessary labour. It is with regard 

 to the fixing of new types that Mendelism gives assist- 

 ance. If the required characters are recessives, they 

 will breed true and will not require fixing beyond the 

 first selection. With dominants, however, it is obvious 

 that ordinary mass selection will give unsatisfactory 

 results, for a considerable percentage of recessives will 

 turn up for a number of years. Mendelism has taught 

 us that the proper method to fix a dominant is to grow 

 the seed of each plant of the second generation sepa- 

 rately. The individuals of the groups which show no 

 recessives will contain no hybrids, and will therefore 

 breed true. We can thus obtain our strain fixed and 

 pure almost at once. 



To turn to the " pure line " theory, we can say that 

 here enough has already been done to show its great 

 value in practice. At the experiment station at Svalof , 

 in Sweden, the isolation of pure lines of cereals has 



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