PHYSIOLOGICAL CORRELATIONS AND CLI- 

 MATIC REACTIONS IN ALFALFA 

 BREEDING 1 



GEO. F. FREEMAN 

 Arizona Agricultural Experiment Station 

 Climatic Reactions 



To the worker who attempts to apply the recognized 

 laws of heredity to the actual operations of plant improve- 

 ment many difficulties arise which heretofore have been 

 largely avoided by students of pure genetics. Color and 

 form characters are but little affected by the immediate 

 ordinary environment and hence, for the sake of simplic- 

 ity, are usually chosen by investigators of heredity. To 

 the economic breeder, however, such characters are of but 

 little consequence except in so far as they indicate phyletic 

 I'd at ion ships. Of greater importance to the breeder are 

 those differences in yield and quality which are the re- 

 sults of inherited, invisible, physiological powers within 

 the plants, whereby each variety may respond differently 

 in manner or degree to the same environmental stimulus. 



Those hereditary units which have to do with vegetative 

 vigor, heat, cold and drought resistance, time of maturity, 

 chemical structure, reproductive strength, etc., are as yet 

 but little understood. This is largely due to the difficulty 

 of exact experiments concerning them. This difficulty is 

 occasioned by the complexity of the reactions of these 

 hereditary forces with the external environment, and also 

 by the direct influence of the development of one part of 

 the plant upon that of some other part. The plant at ma- 

 turity presents the resultant of its environmental reac- 

 tions during development. The nature of these reactions 



iRead before the American Breeders ' Association, Columbia, S. C, Jan- 

 uary 26, 1913. 



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