The persent paper contains a study un the starch content of the chloroplasts of the leaves of Stellaria media, performed by hsitochemical methods. Three leaves were collected at short intervals, fixed and cut in 10 μ sections, and stained according to the PAS‐procedure. The starch content of single chloroplasts was measured by a microscope photometer. The chemical composition of the stainable material was demonstrated by enzyme specific experiments. At the end of a 12 hours' dark period the chloroplasts contained only traces of starch. Light caused the starch accumulation to begin and after a time chloroplasts seemed to be filled with starch. Subsequently, however, a sudden decrease in the starch content of the chloroplasts took place, in spite of constant illumination. A rather high level of starch content was restored in a few hours. The author puts forward some ideas about the nature of the factors causing the transitory disintegration of starch in illuminated leaves. The induction or the activation of certain enzymes seems to be the most probable explanalion. Copyright © 1968, Wiley Blackwell. All rights reserved
