buy new seeds every year. Hybrid corn is offered that has been built up of 

 more "elementary" types of corn, which in turn were obtained by systematic 

 /^-breeding. These plants are small and poor in many ways. But the hybrids 

 are vigorous and combine the desired features of several strains. If you plant 

 seeds /or purple petunias, you will get a handsome growth; but if you plant 

 the seeds from purple petunias, you will get half a dozen or more varieties, 

 but very rarely a purple flower. 



The production of giant blueberries illustrates the range and complexity of 

 problems involved in the creation of new plants. These blueberries are self- 

 sterile. It is therefore necessary to grow them along with another variety to 

 supply the pollen. The plants do not easily form roots on cuttings; this 

 difficulty is met through the use of growth-stimulating substances (see page 

 257). But we do get the giant blueberries. 



Through modern methods of crossing and testing, those interested in 

 special types of plants are constantly producing new varieties with distinct 

 characteristics — early ripening, long fiber, particular colors and flavors, re- 

 sistance to heat or drought, resistance to various diseases, and so on. 



Problems of Animal Breeding In every species of domestic animal 

 there are many more or less distinct varieties. In fact, two artificial breeds 

 of dogs or horses, for example, may differ more, outwardly, than two distinct 

 species in nature. The breeder's first problem is to find the variety or breed 

 that is of greatest value or most suitable for his particular purposes. The next 

 problem is to get the desirable qualities to repeat themselves generation after 

 generation. Those who have to handle cows or sheep, for example, often find 

 the horns in these animals a nuisance. Many farmers therefore prevent the 

 development of the horns by destroying the "button" in the young animal 

 by means of alkali or other chemicals. Occasionally, however, there appears 

 an animal without horns; the Polled Angus was a "sport" of this kind. 

 Polled, or hornless, individuals have appeared also among Jersey and Hereford 

 stocks. If a polled individual is mated with one that has horns, all the off- 

 spring will lack horns. That is, the polled condition is dominant. A purebred 

 hornless bull may thus become the father of whole herds of hornless cattle. 

 But if hybrid polled animals are mated, the following generation will show 

 segregation in the way already described for the yellow-green color contrast 

 in peas and for other plant characters (see illustrations, pp. 476 and 477). 



In sheep-raising certain kinds of fleece are found to be more profitable than 

 others. In order to combine merino wool with hornlessness it would be 

 necessary to find out by means of breeding experiments which characters are 

 dominant and which recessive. In three generations we could then establish 

 new breeds having the desired combination. 



In actual practice the matter is, of course, not quite so simple. Some of 

 the characteristics in which we are interested may depend upon the presence 



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