Pollen is 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.
|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).