Abstract
Seedlings of photo-insensitive varieties of soybean, as well as 3 photo-sensitive varieties, were grafted onto 36 to 41 day-old soybean plants and served as either donors or lreceptors of the floral stimulus. Thus, the productivity of, and the sensitivity of growing points to the floral stimulus were compared between the photo-insensitive and sensitive varieties and within the photo-insensitive varieties. When the photo-insensitive varieties were used as donors, flowering times of the receptor stocks did not significantly difEer with the donor varieties. On the other hand, flowering times of the receptor scions differed significantly with the scion varieties; photo-insen-sitive varieties flowered earlier as receptor scions than the ph.oto-sensitive varieties, and the earliness of the receptor scions was almost in the order of the inherent earliness of the scion varieties. The varietal differences in flowering time of the receptor scions became more conspicuous on the later stock varieties. It was suggested that the photo-insensitive early varieties had acquired the higher sensitivity to the floral stimulus in their growing points than the photo-sensitive varieties, and that the response of growing points to the floral stimulus at the early growth stages could be a causal factor for determining the inherent earliness of the photo-insensitive early varieties.
