178 INTRODUCTION TO BOTANY 



The best way in which to illustrate what modern plant 

 breeding means is to give a few instances of the methods 

 actually employed. 



169. Wheat breeding : its purpose. Wheat is the most im- 

 portant grain for human food in temperate climates, and North 

 America is by far the greatest wheat-producing region in the 

 world. The annual value of the crop of the United States 

 ranges from $250,000,000 to $500,000,000. Scientific wheat 

 breeding began barely a century ago, and has progressed more 

 in the United States since 1890 than during all our previous 

 history. 



Some desirable qualities to be sought in wheat breeding are 

 (1) large yield per acre ; (2) good quality for bread-making, 

 requiring a high per cent of the tenacious gluten, the main 

 protein portion of the grain ; (3) hardiness, shown in winter 

 wheat, in resisting severe winter conditions ; (4) resistance 

 to rust ; (5) resistance to drought. 



Not all of these qualities can be combined in the highest 

 degree in any one variety, and therefore every region should 

 grow the particular kind of wheat best suited to the local 

 conditions and market. About eight species of wheat are 

 recognized, and the number of varieties of these species is 

 very large. 



170. Wheat breeding : the method. In order to show how 

 carefully the process of wheat breeding is managed in our 

 best agricultural experiment stations, the principal steps of 

 the operation are here given in the barest outline, omitting 

 many most important details. 1 



1. Ten thousand large, sound kernels of a single good 

 variety of wheat are selected and planted in hills, and each 

 hill is numbered. About 95 per cent of the poorer plants are 

 rejected as they mature. When mature, the heads of each of 

 the chosen plants are put together in an envelope and preserved. 



1 See Bulletin 62, University of Minnesota Agricultural Experiment 

 Station, and Bulletin 29, Division of Vegetable Physiology and Pathology, 

 U.S. Dept. Agr. 



