Hayes and Garber - Cucurbit Breeding

218 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
+0.46 0.07. The mean winter killing (expressed in percentage)
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.