Single attached leaves of tobacco, depleted of starch, were allowed to assimilate a fixed amount of 14CO2. About 50 per cent. of the 14Carbon assimilated was translocated from the lamina concurrently with assimilation. Of that remaining in the lamina 80 per cent. was incorporated into starch and sugar. Plants were then placed in air and continuous light of different intensities as a means of controlling further starch synthesis. At about 500 f.c. there was no change in amount of starch after 72 hours, but half the radioactivity was lost. At light intensities lower than 500 f.c. percentage activity lost was greater than the percentage amount lost. In sunlight, where new starch synthesis was very rapid, loss in activity from the radioactive portion was prevented. In all circumstances activity virtually disappeared from both hexose and sucrose. It is concluded that starch dissolution proceeded in light even when the amount was increasing. It is further suggested that the loss was mainly from outer layers of the starch grains which were replaced by newly synthesized material. Loss of sugar was by direct translocation rather than passage to starch, and complete replacement by new photosynthate occurred in 24 hours.