Evidence for two types of control of glucose in spinach (Spinacia oleracea L. var. Nobel): mathematical analysis and modelling in short day and during the photoperiodic induction of flowering.- During the lengthening of the short days (8:16 h L:D) light phase, we observe a considerable increase in the content of glucose in spinach petioles immediately after the photoperiodic Iengthening. A mathematical model which describes the experimental data is presented and discussed. This model suggests the existence of two different glucose pools. Accordingly, one of the "compartments" is mainly responsible of the short day pattern, the other being responsible for the pattern obtained during photoperiodic transfer (flower induction)