Abstract: The condition of DNA of sexual cells during development and the process of fertilization in Gossypium hirsutum L., Helianthus annuns L. and Dolichos lablab L., was studied by the Feulgen reaction method. Feulgen negative and weakly reacting nuclei of the female elements of mature embryo sac were studied further with acridine orange induced fluorescence method in order to detect the existence of DNA. The following results are obtained. I. The young egg cells and young polar nuclei or secondary nucleus of these investigated plants give a strong positive Feulgen reaction, when they were newly formed. With the maturation of the embryo sac the Feulgen reaction of these female elements gradually weakened. At the time just before fertilization, the Feulgen reaction of mature egg cell either remained weakly positive (In Gossypium and Helianthus) or became negative (in Dolichos), but the polar nuclei or secondary nucleus always showed negative to this test in all cases. 2. The sperms of above plants always showed a strong positive Feulgen reaction during the whole process of fertilization. As the female elements undergoing fusion and having completed their fusion, they reacted positively to Feulgen again. When the zygotes and primary endosperm nuclei were ready for first division, Feulgen reaction intensified. 3. All these Feulgen negative and weakly reacting nuclei prior to fertilization showed to contain DNA by means of induced fluorescence. 4. The phenomenon of Feulgen negativity and dynamics of DNA of female elements are discussed.