PLANT BREEDING 417 



variety of wheat in 1819, was not based on any general 

 knowledge of the laws of plant variation and inheritance. The 

 principles of breeding, as applied to the small grains, were 

 first worked out by Professor W. M. Hays of the University 

 of Minnesota Agricultural Experiment Station, and by Dr. 

 Hjalmar Xilsson, director of the experiment station at Svalof, 

 Sweden. Some of the main principles upon which wheat 

 breeding depends may be stated as follows : 



(1) Every species of cereal usually comprises many well- 

 marked varieties, or, as they are sometimes called, elemen- 

 tary species. Sometimes there are several hundreds of these 

 included in each of the longest-cultivated species of grain, 

 notably so in the case of wheat. 



(2) The varieties may, while still growing in the field, be 

 distinguished by such botanical characters as the position, 

 shape, size, and bearded or beardless condition of the head; 

 the form, size, and appendages of the spikelets which it con- 

 tains; and the size, shape, color, and hardness of the grain.^ 



(3) The varieties distinguished by such characters as are 

 mentioned in (2) often differ much in their economic value, 

 depending on such qualities as productiveness, resistance to 

 drought, resistance to rust, and the grade of flour which they 

 produce. 



(4) Varieties usually come true from the seed, so that when 

 one has been chosen and isolated it may be grown indefinitely 

 with little change. 



384. Variation in corn. Indian corn is preeminently an 

 American plant. At the time of the discovery of America, 

 and probably for a long period before that time, it was grown 

 by the Peruvians, the ^lexicans, and by many tribes of Indians. 

 It is supposed to have originated in South or Central Amer- 

 ica, near the west coast. The corn plant differs greatly in size 

 and in the time required for maturing. The smallest pop corn 

 is IJ- feet high, while field com has been known to reach a 



1 The hardness cannot be accurately known until the grain is ripe 

 and dry. 



