pollen grain A microspore in flowering plants, which germinates to form the male gametophyte, a structure made up of the pollen grain plus a pollen tube. The grain contains 3 haploid nuclei (a tube nucleus and 2 sperm nuclei), which pass down the tube to the ovum. One of the sperm nuclei fertilizes the ovum, and the second fuses with the 2 polar nuclei forming the endosperm. The tube nucleus (which is considered to be vestigial, having been completely functional earlier in the evolution of flowering plants) degenerates after double fertilization (so called because of the two unions of nuclei).

pollen Yellow, powder-like spores that give rise to the male sex cells in flowering plants. Pollen grains are produced in the anther chambers on the stamen. When the pollen lands on the stigma of a compatible plant, it germinates, sending a long pollen tube down through the style to the ovary. During this process, one of its nuclei divides, giving rise to two male nuclei (the equivalent of male sex cells or gametes), one of which fuses with a female sex cell in fertilization. The other sex cell fuses with two more of the female nuclei to form a special tissue, the endosperm. In many species, this tissue develops into a food store for the embryo in the seed. See also alternation of generations; pollination

pollen The mass of grains containing the male gametes of seed plants, which are produced in large numbers in the pollen sacs. The pollen grains of insect-pollinated plants may be spiny or pitted and are usually larger than those of wind-pollinated plants, which are usually smooth and light. The pollen grain represents the male gametophyte generation; it contains two male nuclei: a generative nucleus and a tube nucleus. The wall of the mature pollen grain consists of the tough outer wall (exine) and the more delicate narrower intine. The latter gives rise to the pollen tube. See also pollination.

pollen Collectively, the mass of microspores or pollen grains produced within the anthers of a flowering plant (angiosperm) or the male cones of a gymnosperm.

pollen Collectively, the mass of microspores or pollen grains produced within the anthers of a flowering plant or the male cones of a gymnosperm. Different pollen types are described according to their shapes, apertures, etc. Furrows on the surface of the pollen grain are called ‘colpi’ (sing. colpus) or ‘sulci’ (sing. sulcus); the words are synonymous. Monosulcate pollen has a single colpus, tricolpate pollens have three, furrow-like colpi (sulci) arranged 120° apart, and there are many variants of this type.