Abstract
In a previous paper 1 data were presented which led to the belief that the comparative resistance of certain plum varieties to brown rot is due to mechanical resistance to the entrance of the fungus. The more resistant varieties had a tougher skin and a firmer flesh; and, at the same time, they had a higher crude fiber content. Preliminary calculations of correlation by rank between skin and flesh texture indicated that the two factors, tough skin and firm flesh, varied together. If this premise could be proved to hold: generally, it would be of value in further work on plums, since only one of the two factors would need to be measured.
A considerable number of measurements of these two constants are now at hand. They cover the three seasons of 1923, 1924, and 1925; they involve over 45 varieties of plums grown at the Fruit Breeding Farm of the University of Minnesota; and they have been taken at all stages of ripeness. These data are presented in the accompanying table.
Each sample, representing a variety at a particular stage of ripeness, consisted of from 4 to 6 plums. The puncture test on the skin and the penetration test on the flesh, as described in the previous paper, were made from 3 to 6 times on each plum. The values used in the calculations were sometimes the averages of the readings on the individual plums, at other times the averages for the lot. In the 1925 material stages III and IV were used both separately and together. In the other cases all stages were included in one calculation.
It is apparent from the magnitude of the coefficients that a very significant negative correlation exists between the values for the two constants.
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