The female gamete and its protective and nutritive tissue, which develops into the dispersal unit or *
seed after fertilization in seed plants. In angiosperms the ovule comprises a central *
embryo sac containing the gamete and other haploid nuclei, the surrounding *
nucellus , and one or two protective *
integuments interrupted by a small opening, the *
micropyle. The ovule is attached to the placental tissue (see
placentation ) by means of the *
funiculus. In most plants the ovule is completely bent around so that the micropyle faces towards the placenta. Such ovules are described as anatropous (see diagram). In some plants, e.g. certain members of the Caryophyllaceae, the ovule is at an angle to the funiculus, which appears to join the ovule midway between the micropyle and chalaza. This is the campylotropous form of ovule orientation. In a few plants, e.g. Polygonum, the ovule is erect or orthotropous. There may be one or many ovules in the locule of an ovary. In gymnosperms the ovule tends to be larger and is borne naked on an *
ovuliferous scale rather than within an ovary. The formation of a cuticle around the ovule of seed plants is a significant development in the evolution of the terrestrial habit.
