Abstract
1. This study was made from June to October in 1950 on the farm field of Hokkaido University in Sapporo, Hokkaido. 2. Principal weed community in this field consisted of 13 families including 29 species. 3. Perennial weeds showed the tendency to decrease towards summer and to increase again towards autumn. On the contrary, the annual weeds proved the opposite tendency to perennial weeds. 4. Regarding the weeds on a field as a plant community, we could make frequency diagrams for each month, and they show that the weed community was stabilized in spring and autumn, and unstabilized in summer. 5. The dominant speciees in each month were as follows: June Agropyron repens, July Euxolus asendens, August The same, September the same, October Agropyron repens. 6. By surveying the each weed on its frequency and covering ratio, I could classify these weeds in five types: Spring Summer type, Summer Autumn type, spring & Autumn type and Spring Summer Autumn type.
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