The ovary contains the ovules. When these are acted upon or fertilized by the pollen they develop into seeds. The pollen falls upon the stigma or upper extremity of the pistil, and each grain germinates and sends a tube down through the style to an ovule. The stigma is a slightly roughened soft surface, and when it is "ripe," or ready to receive the pollen, it becomes slightly moist or sticky. In most plants the stigma is merely a circular expansion of tissue (Fig. 97), but sometimes it is divided into lobes and the lobes remain closed until it is ready for the pollen. The fuchsia stigma is composed of four lobes, which are closed in Fig. 90. Fig. 93 shows the two-lobed stigma of the trumpet-creeper or tecoma before the flower is ready for pollination. Fig. 94 shows the stigma open, in condition to receive the pollen. In these flowers the stamens are hidden in the tube of the corolla. [Illustration: Fig. 92. Staminate Squash flower.] The pollen is nearly always in the form of very small grains, which become dry when ripe. In some plants, notably in orchids, the pollen is borne in large masses known as pollinia. When the anther is "ripe" it assumes a yellow, orange or brownish cast and the pollen is discharged through a split in the side, a chink at the apex or other aperture. The pollen may fall upon and fertilize the stigma of the same flower, in which case the flower is said to be self-fertilized, or oftener it is carried to another flower by insects, winds or other agencies. Most plants possess some contrivance which renders self-fertilization difficult and cross-fertilization easy. [Illustration: Fig. 93. Closed stigma of tecoma.] [Illustration: Fig. 94. Open stigma of tecoma.]