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BREEDING CROP PLANTS 



correlation coefficients. Two nurseries had been planted on 

 succeeding years with the same strains taken from the same 

 original lot of seed. The percentage of killing of the various 

 strains in one nursery during the winter of 1908-09 was correlated 

 with similar data collected from the other nursery after the winter 

 of 1910-11. A correlation coefficient of +0.62 0.06 was 

 obtained. 



Some of the surviving plants of the different alfalfa strains 

 were selfed and the seeds so obtained were planted separately in 



FIG. 53. Comparative hardiness of Grimm and common alfalfas. The two 

 rows in the center are from Grimm seed. At either side are rows grown from 

 southern grown common seed. 1916 season. (Photo loaned by Arny.) 



a third nursery. Percentage of winter killing of these strains 

 was taken and the. correlation coefficient between the percentage 

 of winter killing of the parental stock and that of the new strains 

 was determined. The correlation coefficient obtained was 

 -f-0.46 0.07. The mean winter killing (expressed in per- 

 centage) of the parental stock was 27.43 1.75 as compared 

 with 6.43 0.66 for the strains coming from selfed seed. In 

 other words, progress has been made toward isolating hardy 

 biotypes. 



