EN
Fertile ovules of Oe. hookeri were compared with infertile ovules of Oe. mut. brevistylis. Their anatomy was very similar but maturation of Oe. mut. brevistylis ovules was delayed and they were not ready for fertilization at flowering time. Ovules of both Oenothera taxons divided into sample groups were stained or tested for histochemical reactions: PAS for insoluble polysaccharides, alcian blue for acidic polysaccharides, alizarin red S for free calcium ions, ruthenium red for pectins, and Gomori’s method for acid phosphatase. The ovules were observed under a light microscope. Besides these treatments, ovules from opening buds and flowers were stained with aniline blue and observed with a fluorescence microscope. Other ovules were sectioned and analyzed with an electron microscope. Receptive ovules of Oe. hookeri produced an exudate in the micropylar chamber, clearly visible in TEM. The exudate contained free calcium ions and acidic polysaccharides. The micropylar part of the integuments gave positive reactions for pectins, acidic polysaccharides and acid phosphatase. The substances present in the micropylar part of fertile ovules, especially calcium ions and acidic polysaccharides, perhaps serve as guiding and attracting factors for the pollen tube. In non-receptive ovules of Oe. mut. brevistylis, all mentioned reactions were negative. The staining methods may be used for testing the fertility of ovules.