Etiolated Avena seedlings have been treated with phosphates (P) and light (L) in a factorially arranged experiment. P increased the growth of the mesocotyls by maintaining cell division in the nodal meristem; cell length was not affected. While L inhibited cell division irrespective of the presence of P, a differential effect on cell growth was observed. Without P some few cells remained short after having been illuminated, but no such cells were seen in the plants given P. This difference can be correlated with cell length at the time of illumination. The inhibitory effect of L on mitosis can be disassociated from that on cell growth.