PLANT-BREEDING 335 



ordinary farmer it does not stay improved very long. Unless 

 the farmer uses great care in his own selection of individuals 

 for seed, he will mix poor individuals with good ones and his 

 succeeding crops will degenerate. For this reason, such 

 farmers must apply frequently to the plant-breeders for a 

 new supply of " guarded stock," that is, seeds from individ- 

 uals that have been carefully selected and kept separate from 

 the undesirable ones. 



39. Pedigree culture. Another method of plant-breeding 

 that has come into prominence more recently is called pedigree 

 culture, which means that a single plant is selected and its 

 progeny carefully guarded, rather than hundreds of plants. 

 It is the method ordinarily used in breeding fine animals. 

 For a long time animals have not been improved by the pas- 

 ture-full, but by the individual, whose pedigree is carefully 

 recorded. It is a well-known fact that no two individuals 

 are exactly alike, so that in even the most careful mass 

 culture many kinds of individuals are mixed, and the result 

 is an average. In pedigree culture it is not an average of 

 many good individuals that is secured, but the very best 

 individual. 



The advantages of pedigree culture over mass culture are 

 obvious. The selected individual is farther along in the right 

 direction to start with, and so time and labor are saved; 

 and also it is found that the result is more constant and less 

 likely to degenerate. However, the best results are obtained 

 by combining the two methods ; for even after pedigree cul- 

 ture has selected out a desirable race, it may be improved by 

 mass culture. 



40. Disease-resistance. In connection with pedigree 

 culture it has become possible to combat disease and drought 

 with remarkable success. These are the two most serious 

 enemies to cultivated plants, and our annual losses from these 

 two causes are very large. A few notable cases will serve to 

 illustrate the method. 



