Worlds of David Darling
Encyclopedia of Science
   
Home > Encyclopedia of Science

pollen





tyoes of pollen grains
Pollen grains are found in flowers' pollen sacs, which are themselves located in the anthers (part of the stamens). Pollen grains are safe and effective storers of the male gametes (sex cells). They come in all shapes and sizes depending on the species of plant. The selection shows mistletoe (A), venus fly trap (B), spinach (C), honeysuckle (D), touch-me-not (E), cotton (F), rice (G), dandelion (H), and hollyhock (I).
Powder-like spores, usually yellow in color, that give rise to the male gametes in plants. In angiosperms (flowering plants), pollen grains are produced in the anthers on the stamen, whereas in gymnosperms (cone-bearing plants), they are produced by the male cones. Pollen has thick resistant walls withy a characteristic pattern of spines, plates, or ridges, according to species. During pollination, the pollen lands on the stigma of a flower, or a female cone, of a compatible plant. It germinates, sending out a long pollen tube down through the style to the ovary. During this process, one of its nuclei divides, give rise to two male nuclei, one of which will fuse with a female sex cell (actually a haploid nucleus in the embryo sac inside the ovule) in fertilization. The other male sex cell fuses with two more of the female nuclei to form a special tissue, the endosperm, whose cells contain three sets of chromosomes (triploid). In many species, this tissue develops into a food store for the embryo in the seed.


Related category

   • BOTANY