(b) — Plant Improvement 



In general the three main lines that have been adopted 

 for the improvement of plants are : 



1. Continued selection of superior individual plants 

 {Line Selection). 



2. Separation from mixtures of such individuals as show 

 desirable qualities and breed true to type [mutations). 



3. Combination of the desirable qualities of two strains or 

 varieties by hybridization. 



There are two methods of growing plants for selection, 

 which Webber calls the Nursery Method and the Field 

 Method. By the former "each plant is grown under the 

 most favorable conditions for its best development." By 

 the Field Method "the selections are made from plants 

 grown under normal field conditions.' In order to keep the 

 selected strain up to a high standard, selection must be con- 

 tinued year after year, for unless this is done the plants 

 gradually revert to the normal or average type of the strain 

 before selection began. 



The second line of improvement, viz., the separation of 

 mutations showing desirable qualities, although uncon- 

 sciously used to some extent for centuries, is only now being 

 adopted by breeders, as a result of the studies of DeVries, 

 Bateson, Nilsson, and Burbank. Darwin recognized muta- 

 tions as sports. A practical difficulty exists in our inability 

 to distinguish them from variations of the ordinary sort. 

 The only test is to breed them. Mutations come true to 

 type and do not show any tendency to revert. Ordinary 

 variations are of value mainly in the production of improved 

 strains of a race, which are soon lost when the selection is dis- 

 continued. Mutations or sports, on the contrary, are of 

 value in the production of distinctly new races and variet- 

 ies which maintain their new characters without continued 

 selection." 



Methods of Improvement. — Seven distinct methods of 

 improving old types of cultivated plants and establishing 

 new ones may be recognized: 



1. Hallett's Method. — Plants are grown under the best 

 possible conditions, and the best are selected. This meth- 

 of was first used by Hallett who originated several superior 

 strains of wheat, oats and barley (See Chapter 5). It pro- 



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