572 MAN AS A CONQUEROR 



gated asexually. Burbank's well-known adventure with the potato 

 seed-ball was doubtless due to the fact that the flower which produced 

 this seed-ball had been pollinated from another plant with different 

 qualities from those of the Early Rose potato plant that produced the 

 seed-ball. All that is known of this story is what has been told by 

 Mr. Burbank, how he discovered the seed-ball, watched it develop, 

 and the following year planted its seeds. He tells of the great 

 variation in the offspring which grew from these seeds and of his 

 selection for propagation of the tubers from one of the plants that 

 gave rise to the famous Burbank potato, still one of the most popular 

 products of the potato industry. 



The case just cited illustrates one of the most common methods used 

 by plant and animal breeders today. It has been recognized that 

 two types of variations exist in nature. The first is that of so-called 

 fluctuating variations, seen in all living things, which, for example, 

 result in the bearing of a number of fruits or seeds of different sizes 

 by a single plant, or leaves of slightly differing shape by a tree. Such 

 variations, however, as the agriculturist knows are not handed down 

 from one generation to the next. The second type of variations is 

 called mutations or discontinuous variations. This knowledge has 

 quite revolutionized the methods of plant and animal breeders, and 

 they now attempt to find and propagate mutants, instead of trying 

 to make use of variations that are not capable of being handed down 

 to the next generation. 



Methods used in selection have also changed. We use selection 

 for plant and animal betterment, but we do not necessarily always 

 select the best appearing fruits or largest seeds for future planting. 

 As Donald F. Jones has well said, "Science now shows how a bumper 

 crop of all good ears may be grown from nubbins, but they must be 

 the right kind of nubbins." ^ 



Most important of the investigations in the research program of the 

 Department of Agriculture is the search for a "superior germplasm." 

 When such a superior stock becomes available, it is perfected and 

 the results turned over to the practical breeder for perpetuation. 

 The isolation of strains having superior breeding possibilities is of 

 tremendous value to the farmer because it not only enables him to 

 grow more plants in a given area, but also plants of better quality. 

 In 1935, the parasitic organism, stem rust, cost the farmers in North 

 Dakota alone $100,000,000. Since over 100 strains of black stem rust 



1 JSast, E. M., Biology in Human Affairs, McGraw-Hill, 1931. 



