160 FIELD CROPS 



giving the best returns. A very common method is to grow- 

 on uniform land from one thousand to several thousand 

 plants of the variety of wheat to be improved. At harvest 

 time, twenty-five or fifty of the highest-yielding plants are 

 saved, and the seed from each plant kept in a separate 

 package. With the seed from each of these selected plants, 

 separate plats are planted to test their ability to continue to 

 give large yields. This comparative test is continued for 

 at least three years; the plant giving the highest average 

 yield for three years in the small plat is increased as rapidly 

 as possible, to furnish seed for the main crop. 



200. Crossing. As wheat plants are close-fertilized, 

 crossing artificially is often practiced. To do this, the 

 unopened anthers are removed from the florets and the head 

 is covered for a couple of days until the stigmas are ready 

 to be fertilized. Ripe pollen is then taken from another head 

 and dusted on the stigmas of the head from which the anthers 

 are removed. The head is again covered to prevent any 

 other pollen from reaching it. On account of the fact that 

 wheat is not naturally cross-polhnated, crossing in this way 

 causes a great variation in the resulting plants. The crossing 

 of two varieties of wheat may bring forth plants similar to 

 either parent and many variations from either of the original 

 types, as for example, bearded wheats may result from a 

 cross between beardless varieties. The object of crossing 

 is sometimes to unite desirable characters in two varieties, 

 and sometimes to cause a greater variation than is common, 

 with a view to having greater opportunity for selection. It 

 takes several generations to fix the character of a w^heat plant 

 produced by crossing. A few desirable varieties of wheat 

 have been produced in this way, but by far the greater num- 

 ber are the result of straight selection. 



201. Judging Wheat. For the purpose of judging seed 

 wheat, the agricultural colleges have devised score cards 

 2;iving varying values to the important points desired. 



