1. Radioactive CO2 was fed to plants (Zephyranthes drummondii) which were producing flowering scapes. Subsequently, the ovaries were removed, and autoradiographs were prepared by two different methods. 2. The results indicate that readily soluble carbon-containing compounds are most concentrated in the vascular tissues, in a small area at the point of attachment of the ovule to the funiculus immediately below the hypostase, and in the cytoplasm of the embryo sac. Relatively insoluble C14-containing compounds were most concentrated in the nucellus, the synergids, and the antipodals. 3. Cells of the nucellus lateral to the hypostase divide actively, and cells of the nucellus next to the embryo sac break down during endosperm development. It is probable that the embryo sac obtains much of its nutrient materials from the breakdown of cells of the nucellus.