MUTATION THEORY IN PRACTICAL BREEDING. 63 



lent in grasses and grains as in flowers, but they have not been noticed 

 generally because the external characters which distinguish each newly 

 arisen form from its parent, will be observed in most cases only upon 

 careful examination by a trained eye. Yet the value of these muta- 

 tions in the field crops is economically greater than that of the strik- 

 ing changes that have added to the attractiveness of our flower-gar- 

 dens, because, however small or insignificant may be the external 

 characters by which the several mutants of grass or grain may be 

 recognized, each elementary form has its own characteristic size, shape, 

 weight, number, and nutritive value of the seeds, adaptability to par- 

 ticular climatic conditions, resistance to disease, or the attacks of in- 

 sects, etc.; and some of these new forms are sure to prove distinctly 

 better in some or all of these respects, than those already in cultiva- 

 tion. 



This emphasizes one of the most important gains that come to plant 

 breeding through the recognition of the mutation theory. When 

 sports or mutants are recognized as normal products of a natural 

 process, the eye of the breeder learns to seek for mutational variations, 

 and this search must result in the discovery of many instances of 

 mutation of lesser magnitude though possibly of even greater eco- 

 nomic value than was formerly required to force themselves upon 

 his attention. He will also look for mutations in plants whose indi- 

 vidual characters had before passed almost unnoticed. It is plain, 

 therefore, that the greatest advance to result from the mutation theory 

 will be made in the breeding of those economic plants in which the 

 individual loses itself to a great extent in the population, as is the 

 case in the field crops, for in these it indicates the desirability of 

 handling the individual in much the same manner as it would be 

 handled in the development of a new variety of flowers. 



In the various grass, grain, clover, cotton, and other field crops 

 that are raised from seed, most of the work of improvement has been 

 carried forward thus far on the basis of mass-selection instead of indi- 

 vidual selection, the chief incentive to this method being the general 

 belief in the injurious effects of in-breeding. Many excellent gains 

 have been made by this method, but it is now obvious that it is not 

 calculated to produce either the best attainable result or the largest 

 return for a given expenditure of energy, and these are the prime 

 economic considerations. Eimpau required twenty years for the iso- 

 lation of the famous Schlaustedt barley which has added so largely 

 to the value of the German barley crop, and this length of time was 

 consumed because he did not realize that his problem was one of 

 isolation instead of fixation. It is probable that the use of some good 

 isolation method would have accomplished an equal result in one- 

 fourth the time. 



Every method which carefully tests the transmissible characteristics 

 of the individual, and bases its selections upon performance records 

 is in essential harmony with the conception that each economic variety 

 is a composite group of distinct elementary forms that have origi- 



