PRINCIPLES AND METHODS OF PLANT-BREEDING 137 



Morgan horse was a result of mutation, and it is definitely known that a 

 large part of racing stock may be traced back to one exceptional, original 

 parent. It is not unreasonable to suppose that some of our great families, 

 in the human race, may have originated in this way. ' Farmers should be 

 always on the lookout for these striking forms of variation. Mutations 

 are constantly occurring among plants, but they cannot be made of use 

 unless some one observes and saves them. 



Methods of selection 



There are two methods of selection that have been used. The first 

 of these is mass selection and the second is individual selection. Both 

 these methods are in use, although the first method is not nearly so good 

 as the second. 



Mass selection. Mass selection is probably the method used most by 

 farmers. It consists, usually, of a selection of good-looking individuals, 

 without special regard to the performance record of the parent plants. 

 Individual performance records cannot be obtained because the seed from 

 these individuals is mixed together " in a mass " and then sown. Some- 

 times it is sown in a part of the field set aside for seed purposes and is 

 given special care and attention. The plants from this seed represent 

 many different families. The plant-breeder calls them strains, or types. 

 Some of these strains, or types, are good yielders, others are medium, and 

 still others are poor. In fact, there are all gradations of excellence. By 

 practicing mass selection persistently, the poorer types may gradually 

 become eliminated and the better types left. This process would take 

 years, however, and in many instances would be doubtful of accomplish- 

 ment even then. Isolation and conservation may be accomplished much 

 more readily by individual selection. 



Individual selection. It has been said that there is always variation 

 among plants, that no two plants are exactly alike although they may 

 belong to the same species. There are families of plants just as there 

 are families of people; not the families of which the botanist speaks, but 

 the types and strains of the plant-breeder. Every plant possesses its 

 own individuality or characteristics. These characteristics are of the type, 

 or strain, to which the plant belongs. It is by a study of individual plants 

 that these different type traits can best be noted and conserved. This 

 is what is meant by individual selection. Thus we have "ear to row," 

 . " head to row," and "tuber unit " methods of conducting breeding plots. 



The " ear to row " method in corn furnishes a means for testing the 

 individual capacities of ears of corn. The same number of kernels from 

 each of one hundred ears are planted in one hundred separate rows. The 

 rows are all of the same length and are treated as nearly alike as possible. 



