l.MPROVEMEXT OF FIELD CROPS 1 9 



crops, just as there now are many breeders of pure strains of 

 domestic animals. 



38. Methods of Improvement. — There are three steps or 

 methods in the improvement of plants or animals, viz.; 



A. Inducing variation. 



B. Selection of forms having desired characteristics. 



C. Testing the power of specific forms to reproduce them- 

 selves. 



39. A. Inducing Variation. — ^^^ariation is the basis of selec- 

 tion. Plants must \3.ry or they could not be selected. There 

 are two general methods of producing variations, viz.: 



1. Environment, such as soil, climate, space, cultivation, etc. 



2. Crossing. 



40. The Influence of Environment. — The causes of variabil- 

 ity cannot be discussed here, but the following facts should 

 guide the breeders of plants. 



1. Horticulturists do take advantage of a superabundance 

 of food in causing modification or multiplication of parts, such 

 as the development of petals from stamens. After this habit 

 becomes fixed it will be transmitted in some measure even in 

 poor soil. 



2. Nevertheless the most important value of cultivation in 

 the case of most plants is to allow the plant breeder or cultivator 

 to study individual forms. It enables him to select the desirable 

 forms and reject the undesirable ones. By milking the cow and 

 testing her milk we are able to select the best milkers. By 

 trotting horses we are enabled to breed those best able to trot. 

 Whatever influence milking or trotting may have, the fact 

 remains that it makes possible intelligent selection. 



3. The variations selected should be those induced under 

 the environment in which we expect to continue to grow the 

 crop. If we expect to grow three stalks of maize to the hill in 

 general field culture, it is desirable to select the ears for plant- 

 ing from maize grown in a similar manner, rather than from ears 



