METHODS OF IMPROVEMENT 159 



pose of all rubbish in the fall, so that the bugs will have fewer 

 places in which they may be able to hibernate. 



(c.) Grasshoppers when abundant, often do great damage 

 to wheat. The eggs are laid in the ground during midsum- 

 mer, and hatch the following spring. The young hoppers 

 have no wings; hence the}^ do not travel about much. 'When 

 full grown they acquire wings and fly readily. The eggs 

 are usually laid in pastures, meadows, and in waste land. 

 Late fall plowing and rotation of crops are effective in con- 

 trolling the hoppers, for many of the eggs are destroyed and 

 others are buried so deep as to prevent the young hoppers 

 from getting to the surface when hatched. The young hop- 

 pers are often destroyed in large numbers, by use of hopper- 

 dozers, or by poisoning with arsenite of soda. 



((/.) Army worms sometimes injure the growing crop, 

 while grain weevils are destructive to the stored grain, es- 

 pecially in the South. These insects and the remedies for 

 them have already been discussed (Section 146). 



METHODS OF IMPROVEMENT 



198. Wheat Will Not Mix. Wheat, being close-fertilized, 

 is one of the comparatively easy crops to improve, because 

 selected plants do not become mixed with undesirable ones, 

 as is the case with corn. It is probable that occasionally 

 some cross-fertilization occurs, but it is so seldom as to be 

 unimportant. If several varieties of wheat are grown in 

 one plat, any one plant will produce pure seed regardless of 

 the plants surrounding it. This fact enables one to use 

 large numbers of individual plants in improvement work. 



199. Breeding by Selection. The most common method 

 of improving wheat is by selection. A large number of 

 wheat plants grown under perfectly uniform conditions will 

 vary greatly in yield and in other respects. Advantage 

 should be taken of this fact in breeding by eliminating all 

 the poorer plants, and reproducing only those capable of 



