Journal of Agricultural Research . for the infection of the plants nearestto them, but the many small infected areas (appearing at the samedistance from the old periphery) soon merged into a regular band com-pletely circumscribing the old area of the previous year (pi. 4, B). The 414 Journal of Agricultural Research Vol. XXVI. No. 9 infection then spread centripetally as well as centrifugally, and it fre-quently happened that the majority of the plants reestablished insidethe old areas during the fall and winter were killed by this retroactiveinvasion. The map shown in Figure 4 shows the locat
Journal of Agricultural Research . for the infection of the plants nearestto them, but the many small infected areas (appearing at the samedistance from the old periphery) soon merged into a regular band com-pletely circumscribing the old area of the previous year (pi. 4, B). The 414 Journal of Agricultural Research Vol. XXVI. No. 9 infection then spread centripetally as well as centrifugally, and it fre-quently happened that the majority of the plants reestablished insidethe old areas during the fall and winter were killed by this retroactiveinvasion. The map shown in Figure 4 shows the location of activity in the 9-hectare field during the seasons of 1921 and 1922. It will be noted thatwith the great majority of rings the diseased area of the succeedingyear seems to be merely an extension of the centrifugal spread of theprevious season. Some of the spots, however, showed no renewed infec-tion in 1922. The largest areas, which showed indications of havingbeen active longest, seemed to show a tendency toward
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Keywords: ., bookauthorassociationoflandgran, bookcentury1900, bookdecade1910
