Accoring to the criterion of developmental stages established in the preceding paper (FUKUl, J, and GOTOH, T., in press), the authors intended to make clear the effect of day-length and temperature upon the development of floral organs and its varietal differences. Sango-wase-daizu (early variety, Ia), Norin No. 2 (rriiddle variety, Ilb) and lpponsuzunari (1ate variety, Vc) were cultivated in fcur plots, that iscontrol plot (natural day-1ength, in outdoors), shortday plot (10-hours day-length in outdoors), high temperature plot (natural day-length, in greenhouse which is 3-4°C higher than outdoors) and short day high temperature plot (lO-hours day-length, in greenhouse). Ia, Ilb and, Vc are symbols of ecolo gical types as deflned by FUKUl, J. and ARAI, M. (1951). In control plot, Sango-wase-daizu bore flower primordium 10 days after cotyledon unfolding and floral organs developed rapidly. Norin No. 2 and lppon suzunari bore flower primordium 24 days after cotyledon unfolding. The development of floral organs was faster in Norin No. 2 than in lpponsuzunari.The development of floral organs of lpponsuzunari was very slow, especially inl early stages (from stage1 to stage ll). The day-length was capable to in duce the flower primordium formation but it was too long for the normal development of floral organs. As plant age proceeded, plants became more sensitive to day-length, so fioral organs developed slowly to stage 11. After stage 12, floral organs developed at the normal rate and soon flowering occurred, since the process after stage 12 was in.sensitive to day-length. By short-day treatment, both flower primordium formation and development of floral organs were accelerated in the all varieties, the degree of acceIeration being larger in late variety, rather little, in middle variety and little in early variety. In the developmental course of floral organs, the early stages, that is, from stage 1 to stage 11 hours) day-length, the flower primordiuirl formation was accelerated in Sango-wase-daizu and Norin No. 2 the critical day-lengths of which were longer than 14.5-15 hours. In lpponsuzunari the critical day-elngth of which was near 14.5-15 hours, the flower primordium formation was rather reta.rded. The developmen.t of floral organs was accelerated in the all three varieties. By the elevation of temperature under 10 hours day-1ength, the flower primordium formation was accelerated in Sango-wase-daizu and lpponSuzunari, but not in Norin No. 2. The development of floral organs was accelerated in all the three varieties. The acceleration of development of floral organs by the elevation of temperature was general but an especially sensitive stage ivas not obvious.