. Damping-off in forest nurseries. Plant diseases; Trees. 50 BULLETIN 934, U. S. DKI'AKTMKNT OK the horizontal line showing the locution of the mean for experiment 68 are much larger below the moans than above it in the left-hand portion of the graph, while the reverse is true in the right-hand portion. To this extent the relative activity of the strains in this experiment agrees with the performance of the same strains in the two jack-pine experiments, as shown by the solid line. It can not be decided from an inspection of the graph whether there is a real agreement, in view of
. Damping-off in forest nurseries. Plant diseases; Trees. 50 BULLETIN 934, U. S. DKI'AKTMKNT OK the horizontal line showing the locution of the mean for experiment 68 are much larger below the moans than above it in the left-hand portion of the graph, while the reverse is true in the right-hand portion. To this extent the relative activity of the strains in this experiment agrees with the performance of the same strains in the two jack-pine experiments, as shown by the solid line. It can not be decided from an inspection of the graph whether there is a real agreement, in view of the large accidental variation present. How- ever, the correlation coefficient, + , five and one-half times its probable error, indicates a considerable correlation, not as good as was found for the Cbrticium strains, but sufficient to establish a strong presumption that observed differences in activity of the dif- i I A /•%. I A / S / i 1 J \ j^AYJrJff- M£#/V eXPTS. 66/7/VO 67 ill' I L_l l_ 'I'll' m\ Fig. 16.—Diagram showing the comparative virulence of 47 strains of Pythium debaryanum in successive inoculation experiments on species of Tinus. The results in experiments Nos. 66 and 67 (on Pinus banksiana) are shown by the solid line, the strains beinj; arranged from left to right in the order of descending virulence indicated by the number of seedlings surviving in those experiments. The results from the use of the same strains in experiment No. 68 (on Pinus resinosa) are shown by the broken line. Such correlation as there is between the two curves (coefficient ±) goes to indicate a real difference in virulence between the different strains. The strains indicated by (he underscored numbers are original strains,-and those not underscored are reisolations from the original strains in earlier inoculation experiments on pine seedlings. ferent strains in these inoculation experiments were in part actually due to differences in the capacity of the strains. I
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