The male
gametes of
seed plants, which are produced in the
stamens of flowering plants and in the male cones of
conifers and other
gymnosperms.
To ensure fertilization, the pollen must be transferred to the
stigma (in flowering plants) or the female cone (in conifers) - the process of pollination.
Many flowers are cross-pollinate, ie. the pollen of one plant is deposited on the stigma of another of the same species by animal carriers (usually
insects), wind, or water.
Some flowers are self-pollinated, the pollen being transfered from the
anthers to the stigma of the same plant.
After pollination, a
pollen tube grows down from the pollen grain into the
pistil of the pollinated flower until it reaches the
ovule. Two pollen nuclei travel down this tube: one fertilizes the
egg cell, which develops into the
embryo plant in the seed; the other fuses with a nucleus in the ovule to become
food for the seed.
I am informed by vivid that "pollen grains aren't gametes. They are actually gametophytes, which produce gametes."
My A-Level Biology has failed me, and I stared at my /msg with a puzzled expression on my face for some time.
A quick trip to britannica.com later, and we have this:
"in certain plants, sexual phase (or an individual representing the phase) in the alternation of
generations--a phenomenon in which two distinct phases occur in the life history of the plant, each
phase producing the other. The alternate, nonsexual phase is the sporophyte.
In the gametophyte phase, male and female organs (gametangia) develop and produce eggs and sperm
(gametes), which unite in fertilization (syngamy). The fertilized egg (zygote) develops into the
sporophyte phase, which produces numerous unicellular spores. These, in turn, develop directly into
new gametes. Almost the entire life cycle of many algae and fungi is gametophyte; in others it is almost
all sporophyte."
I'm no closer to understanding this to be perfectly honest with you, but the facts seem to be on vivid's side.