Plant-Breeding for Farmers. 137 



tive propagation in general. A change of environment may cause appar- 

 ently stable races to break up and vary considerably, especially when such 

 races are of hybrid origin or are highly bred sorts. A radical change of 

 environment may, therefore, in some cases lead a plant to break up and 

 produce certain variations that we desire. 



The recent investigations of Dr. MacDougal indicate that we may be 

 able to induce or stimulate a plant to produce mutations or sports through 

 the injection into it at certain periods, of chemical salts. This, however, 

 is at present a field of experimentation for the scientist rather than 

 for the practical breeder. 



One of the mo>t fruitful ways of causing variation is by hybridization, 

 but owing to the complexity of breeding work of this kind it will not be 

 discussed in this paper. 



Principles of selection. 



The keynote of improvement by selection is the choice of the very 

 best individuals. The discovery of the best individual in any crop under 

 consideration, requires the growing of a large number of individuals under 

 as uniform conditions as possible, so that the experimenter may have op- 

 portunity to examine and select the best. Two methods of growing plants 

 for selection are in general use which may be termed i, the Nursery 

 method and 2, the Field method. 



The Nursery method, which so far as the writer is informed was first 

 used by Hallett about 1868, consists in cultivating each plant under the 

 most favorable conditions possible for its best development. By this 

 method with wheat, for instance, Hallett pursued the policy of planting 

 the individuals in squares a foot apart, which would give each plant 

 abundant opportunity for stooling, and also the investigator an oppor- 

 tunity to clearly distinguish each individual plant and determine its 

 characteristics, total yield, and the like. In recent years this method of 

 growing the individual plants at a standard distance from each other in 

 order to test their yielding capacities, and the like, has been used by 

 Professor Hays in his experiments at the Minnesota Station. Here, 

 however, a standard distance of four inches apart was used instead of one 

 foot. 



The Field method was used by Rimpau about 1867, and probably by 

 many others before that time. By this method, the selections are made 

 from plants grown under normal field conditions. The claims for this 

 methofl is that we can only judge what a plant will do in the field under 

 ordinary conditions of field culture, by growing and selecting it under 

 these conditions. In the large majority of cases the first selections are 

 probably made from plants grown in the field in the regular course of 

 crop production, which thus were not specially grown for the purpose. 



