No. 570] 



ALFALFA BREEDING 



357 



is determined by the structure of the vital forces within. 

 These differences in vital structure may or may not be 

 accompanied by visible morphological differences. Such 

 cases of correlation have been known and used in selecting 

 for qualities which they were thought to indicate. The 

 much quoted example of the supposed correlation between 

 the short-haired rachilla and high brewing quality in bar- 

 ley is a case in point. It has been found, however, that, 

 whereas, in one strain or race the correlation may hold, in 

 another, the two characters are in no way related. 

 Another case of similar nature is the coupling of cob and 

 pericarp color in certain varieties of corn and their com- 

 plete independence in others. Many other examples could 

 be adduced to show that the coupling of two characters in 

 a given race of plants is no indication that these same 

 characters are inseparably linked in all races of the same 

 species. These facts have greatly reduced the value for- 

 merly ascribed to gametic correlations in plant breeding. 

 Under our present knowledge, therefore, we must depend, 

 for the most part, upon direct experimentation, rather 

 than correlations, to discover the hereditary physiological 

 characters of the varieties with which we are working. 

 Any additional light, therefore, which may be had con- 

 cerning the nature of such characters, together with meth- 

 ods for the study of the behavior of the same in their rela- 

 tion to each other and to their physical surroundings, will 

 have not only a scientific value, but will also fill a distinct 

 practical need. 



As an illustration of such a study we may now examine 

 the data concerning the development, yield and chemical 

 composition of forty-four regional varieties of alfalfa 

 which were grown on the Experiment Station Farm at 

 Phoenix, Arizona, during the season of 1910. In the case 

 of this plant, which occupies the ground throughout the 

 year and from which six or seven crops may be harvested 

 during the growing period, the climatic factors include a 

 long series of variations coincident with the changing sea- 

 sons. Now, since every variety consists of its own pecul- 



