Application of Biological Principles to Plant Breeding 133 



isolated plots the plants are often intercrossed. Each prize 

 plant selected for future breeding will have had a few and 

 possibly many of its ovules fertilized by pollen from less 

 desirable strains. When these seeds are grown they of 

 course again fertilize the ovules of the desirable plants with 

 a frequency proportionate to their number. In certain 

 plants the process may be shortened by having recourse 

 to artificial self-pollination. But unfortunately this cannot 

 alwavs be done. Suppose one were dealing with red clover 

 where the flowers are small, almost sterile with their own 

 pollen and produce only one seed. In such a crop a long 

 and tedious method of continuous selection must be used 

 for there is no other way. One must simply keep in mind 

 the supporting principle of all selection work, that the 

 seeds of single plants are grown in isolated plots and the 

 character of the mother plant is judged by the characters 

 of the progeny. 



We have already seen from Mendelianism and the geno- 

 tj-pe conception of heredity why this method is the only 

 proper one, but perhaps an illustration will show the 

 matter more clearly. The older method of selection, called 

 variously the German or "mass selection" method by plant 

 breeders and the "performance record" method by stock- 

 breeders, is based entirely upon the appearance or general 

 character of the mother. For example, the German sugar 

 beet raisers have for years analyzed large numbers of 

 suo-ar beets and have grown their seed from the mother 

 beets showing the highest percentage of sugar. No par- 

 ticular attention was paid to planting from "blood lines" 

 of high sugar content; those beets were bred from which 

 appeared to be the best by their performance record in the 

 polariscope test. A great many of these selected mothers 



