Immature sugarcane propagated by sand culture was treated with a single concentration of Polaris (N,N-bis [phosphonomethyl] glycine) at different hours of the day. Plants harvested 21 days thereafter showed significant growth and qualitative differences relating to the amount of sunlight received prior to chemical application. Ripening efficiency was progressively improved as the treatment time was delayed from 0630 to 1630 h. Growth repression was decreased as treatment time was delayed from 0630 to 1830 h. These trends were not appreciably altered by darkening the plants throughout the following day. Preillumination effects are tentatively explained in terms of a Polaris-stimulated transport of hormone-like substances diurnally activated or depleted in leaves. Tissue sucrose levels and acid invertase were extremely sensitive to Polaris but not to the hour of its reception. Foliar trehalase was increased by Polaris and further increased by applying it later in the day.