In Samolus parviflorus Raf. long day induces flowerbud formation and increases stem length directly. Suboptimal induction by long day is completely desinduced by subsequent short day. High temperature, 40°-45°C, when applied during 6 hours in the middle of the light phase of short day, has no flower inducing effect, but when applied in the middle of the dark phase it leads to complete induction. This similarity to Silene armeria L. suggests that also in Samolus parviflorus flower formation depends on two processes: light removes a blocking, darkness has a reblocking effect, but high temperature prevents this reblocking. The inductive effect of GA3 on flower formation was confirmed. Although high temperature in the light does not induce flowerbud formation, while in the dark it induces completely, both applications in combination with GA3 have a pronounced stem elongating effect. Hence S. parviflorus offers another case of separating flowerbud formation and stem elongation.