Flowering inLathyrus macrorhizustakes place the whole year round, irrespective of photoperiod. Minimum flower production often occurs at the end of a spell of continuously decreasing air temperatures and is always preceded by a heavy rain period; the length of time following the end of this period is inversely proportional to air temperature. Maximum flower production often occurs at the end of a spell of continuously increasing air temperatures and is always preceded by a period of drought. It is suggested that flowering cycles correspond with cycles of metabolic activity in tubers, depending on respiratory gas exchanges and on temperatures. [Journal translation]