pollen tube The tube formed from a germinating pollen grain, and down which the 2 male gametes (sperm nuclei) pass to the ovum. In flowering plants each pollen tube penetrates the tissues of stigma and style into the ovary where it grows towards an ovule, passing down the micropyle to the nucellus and finally penetrating into the embryo sac. Here the tip of the tube ruptures, releasing the 2 male gametes: one of these fuses with the nucleus of the ovum; the other fuses with the 2 polar nuclei to give rise eventually to the endosperm.

pollen tube An outgrowth of a pollen grain, which transports the male gametes to the ovule. It will only grow if the pollen grain is compatible with the female tissue. In angiosperms, the pollen grain is deposited on the stigma and the pollen tube grows down through the style and into the ovule. In some conifers, e.g. Pinus (pines), the pollen tube penetrates the nucellus but does not develop further until the following year, when the female part of the plant is mature. See also embryo sac; fertilization; tube nucleus.