In this experiment, the author selected two important low-land rice varieties, Rikuu No. 132 and Norin No. 1, which were registered respectively in 1921 and 1931. The former was reared at Rikuu Branch of the National Agricultural Experiment Station from the cross between Rikuu No. 20 and Kamenoo No. 4, and spread widely in northern part of Japan or used for early cropping system and double cropping system in southern part, and cultivated more than 400,000 hectares in 1939. The latter was selected from the cross between Morita-wase and Rikuu No. 132 in the local rice breeding center of the Niigata Prefectural Agricultural Experiment Station, and extended its cultural area into northern part of Japan or double cropping system in Kochi prefecture, and reached more than 100,000 hectares immediately after its registration. In 1940, the author collected 23 samples f or the former variety and 21 ones for the latter from various parts of Japan and Korea. Selected seeds of these samples were used for direct sowing cultivation on the low-land rice field sowed late May. In the first year, degree of variations of the local strains was recorded concerning date of earing, length of culm and ear, number of ears per plant, and number of leaf on main culm. Parallel variations were found between both varieties, but the magnitude of variation for each character was greater in the older variety namely Rikuu No. 132 than the younger variety, Norin No. 1. Further, large departure of variation was apt to occur in the distantly delivered materials. In the next year about half of the local strains were repeatedly tested in the same cultural condition, but in this case two earliest and two latest individuals from each strain for date of earing were treated, then total lines were 48 for Rikuu No. 132 and 43 for Norin No. 1. Analysis of variance for the date o f earing in the second year materials confirmed that these were found highly significant variations among total lines, between local strains and among intrastrain lines (See Tables 5, 6 and 10). Some detailed data were compiled in the next table.【table】
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