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; (8) hardiness, shown in winter 
wheat, in resisting severe winter conditions; (4) resistance 
to rust; (9) 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. 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. 
1See Bulletin 62, University of Minnesota Avricultural Experiment 
Station, and Bulletin 29, Division of Vegetable Physiology and Pathology, 
U.S. Dept. Agr. 
