24 PRINCIPLES OF PLANT BREEDING 



often try to make use of such sports in the establishment of new 

 types better suited to the uses of man, and perhaps better suited 

 to the environment. The object of using such sports, when it is 

 found possible to do so, is that much time is gained in establishing 

 new types. Certain it is that successful results have been attained 

 through their use, in breeding both animals and plants. 



Reversion. This is the tendency found among both plants 

 and animals for the offspring to exhibit characteristics of different 

 ancestors which the more immediate ancestors did not show. The 

 tendency to reversion is usually detrimental to the progress of 

 the work of the scientific breeder. It brings results contrary to 

 his expectation and perhaps contrary to his ideals. 



Environment. The principle of selection is the one most 

 commonly used by the scientific breeder. It is believed by many 

 scientific breeders that environment or surroundings of the indi- 

 vidual, is a vital cause of variation. There is no doubt that en- 

 vironment has a vital influence upon the results obtained from 

 the growth of certain farm crops or certain domestic animals. 

 Seeds that are of the same origin, planted on different farms, may 

 produce very different yields. Just as fertilizer and tillage may 

 influence the development of a crop, so may feed and other en- 

 vironment influence the development of animals. A litter of pigs 

 if divided into equal lots at weaning time may show variations in 

 their growth during the next few months, due to difference in 

 feed or other conditions. Differences would likewise be noticed 

 if we plant all the beans borne by one bean-stalk. 



To what extent these differences, due to environment, will be 

 inherited by the offspring is a matter of contention among scien- 

 tists. Most modern breeders act upon the principle that extremes 

 of variation, due to environment, do influence the offspring to 

 some extent. 



Prepotency. The power of individual animals or plants to 

 impress certain characteristics upon their offspring is called pre- 

 potency. Use is made of this in scientific breeding. Characters 

 thus fixed may be spoken of as dominant characters. But pre- 

 potency means more than dominance of character, for certain 

 individuals have the power of fixing many of their characteristics 

 upon their offspring. 



Selection. The breeder of plants or animals must carefully 

 practice selection; indeed his greatest skill must be exercised along 

 this line (Fig. 17). After the several lines of variation in any type 



