CHAPTER XVI 



SYSTEMATIC IMPROVEMENT OF PLANTS 



Improvement by selection • Crossing to produce new varieties • Application 



of Mendel's law in crossing • Separation of the desired character • Behavior 



of the recessive • Behavior of the dominant • When more than two characters 



are involved • Systems of planting • Records 



The whole question of practical methods of plant improve- 

 ment rests on an entirely different basis than that of animals. 

 The evolutionary principles involved are identical, but the eco- 

 nomic conditions are different, indeed almost opposite. 



Animals are relatively few in number and costly both in breed- 

 ing and in maintenance. Plants, on the other hand, are cheap, 

 and the numbers may easily run into the thousands, all of which 

 warrants methods in plant improvement that would be entirely 

 impracticable with animals. 



Improvement by selection. Plants, like animals, are subject 

 to improvement by the ordinary methods of selection ; indeed, 

 much improvement is effected in that way. Farmers keep up 

 the quality of corn by selecting for seed the occasional superior 

 ear. The best wheat is chosen for seed and carefully screened 

 of inferior kernels. In this general way we are constantly 

 practicing selection. 



A new method of increasing yield of corn consists in planting 

 selected ears, each in separate rows, carefully harvesting each 

 row separately. Though the ears may have looked identical, the 

 crop will vary greatly. That from some ears will be nearly uniform 

 as to size and character of ear, while that from others will be 

 exceedingly uneven, with many nubbins and inferior ears. The 

 yield, too, will vary greatly, often running more than two to one 

 in favor of certain ears, though they bore no visible indication 



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