Nearly all land plants have alternating diploid and haploid generations. Gametes are produced by the gametophyte, which is the haploid generation. The female gametophyte produces structures called archegonia, and the egg cells form within them via mitosis. The typical bryophyte archegonium consists of a long neck with a wider base containing the egg cell. Upon maturation, the neck opens to allow sperm cells to swim into the archegonium and fertilize the egg. The resulting zygote then gives rise to an embryo, which will grow into a new diploid individual (sporophyte). In seed plants, a structure called ovule, which contains the female gametophyte. The gametophyte produces an egg cell. After fertilization, the ovule develops into a seed containing the embryo.