CHAPTER 9 



CROP IMPROVEMENT 



BY C. F. NOLL 

 Assistant Professor of Agronomy, Pennsylvania State College 



The development of varieties and strains of our farm crops which 

 have great productiveness or superior merit in other respects is a matter 

 of great interest to all agriculturists. Increase in yield due to natural 

 productiveness of a variety results in a gain which is maintained year 

 after year without additional cost of fertilizer or expense in culture. 

 Such gains are of much economic importance, as shown by the differences 

 secured in many variety tests. At the Pennsylvania State College Experi- 

 ment Station, where varieties of various crops are tested under the same 

 conditions there are some which outyield others by as much as fifty per 

 cent. Here the good yielding varieties are grown with just the same 

 expense as the poor ones, except for the slight additional cost of handling 

 the increase in crop. Similar results have been secured at experiment 

 stations in nearly every state. . 



Plant Selection. Crop improvement or plant breeding is oi 

 looked upon as a new thing, but ever since man has been growing plants, 

 they have gradually been modified by seed selection. All of our culti- 

 vated plants come from wild forms, but some of them have been so changed 

 that they could not now perpetuate their race if left to shift for then 

 selves Within the memory of men now living, the fruits of tomatoes 

 have been developed from the size of a walnut to several times as large, 

 and other changes have been effected which have made them more desir- 

 able for table use. Though plant improvement has been thus going on 

 for ages, only within the past few decades has there been great genera 

 interest in this work, and only of late have some of the fundamental 

 principles been understood. . 



Man originates to a very limited extent desirable changes in the 

 plants with which he works. He is dependent chiefly upon changes 

 which occur naturally, and all that he does is to take advantage of these 

 changes and perpetuate the forms which are the most suitable for his 

 purpose. He cannot, for example, make the pole lima beans over into 

 the dwarf form, but when dwarf plants are found in a field of lima beans 

 he can save seed of these plants and perpetuate and multiply a rac< 



dwarf lima beans. 



Kinds of Variation. No two plants are exactly alike, but most ol 

 the variations are of no significance to the plant breeder. They may be 



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