No. 570] 



ALFALFA BREEDING 



363 



(July and August), the American and Turkestan varieties 

 were comparatively inactive, yielding only about eight 

 hundred pounds of dry hay per acre, as against more than 

 » ton and a half each on the first cutting. The relative 



ield curve for the Peruvian type stands separate and dis- 

 tinct from the others. Although here, as with other varie- 

 ties, the yield declines with the advance of the season, the 

 persistence and vigor with which this strain resisted the 

 summer heat and drought caused it to gain rapidly on the 

 other varieties in relative yield throughout the season 

 until the very last cutting, when there was a slight decline. 



Disregarding the shape of the curves we may now notice 

 the total yield for the season. In this respect the different 

 regional varieties take the following relative order : Peru- 

 vian, European, Turkestan, American and Mediterranean. 

 It is here noticeable that, though the European and Medi- 

 terranean varieties have similar seasonal yield curves, 

 they are not contiguous in the arrangement based on total 

 yields. This is a result of a marked difference in the 

 stand maintained by the two varieties which averaged 

 ninety-two per cent, for the former and seventy-four per 

 cent, for the latter. In their ability to maintain stand, the 

 Peruvian, European, Turkestan and American varieties 

 were about equal, averaging 92, 92, 93 and 94 per cent., re- 

 spectively. The lack of stand on the part of the Medi- 

 terranean alfalfas was not due to the poor quality of the 

 original seed, for all of these plots once had perfect stands. 

 This behavior is also in accordance with the records of 

 other fields of Mediterranean alfalfa in the southwest, 

 which have come under the observation of the writer. The 

 explanation of the weakness of the Mediterranean and 

 corresponding strength of the otherwise similarly reacting 

 European alfalfa in maintaining stand under Arizona con- 

 ditions is a subject for further careful physiological study. 



The recognition, analysis, and calibration of these dif- 

 ferences of the physiological reactions of varieties are 

 thus seen to become a first essential in the study of cli- 

 matic adaptation, and form the basis for rational pro- 

 cedure in the choice of varieties and in selective breeding 

 for the improvement of the same. 



