At 1:18 AM -0500 11/17/99, JAMES C. DAVIS wrote:
>What are the advantages to having a motile sperm as to having a pollen
>grain to fertilize an egg?
Well, a motile sperm is a relic of evolution,
not unlike our coccyx. Gametes of modern flowering
plants lack motility as the plants evolved from
aquatic to terrestrial life. It really doesn't matter
much how the sperm and egg get together, just that
they DO and do so RELIABLY. Angiosperm sperm do not
need any free-water to arrive at the egg.
Gymnosperms are mixed as to whether the sperm have
or lack motility. The plant produces the fluid needed
if the sperm are motile. In ferns and fern allies the
sperm are motile but rely upon the environment for the
fluid in which to swim.
Please note: pollen grains do NOT join with the egg.
This is a common misconception. The pollen grain is
an endosporic microgametophyte consisting of two or
three haploid cells. The growth of the pollen tube
delivers two sperm cells to the embryosac. One of the
two sperm joins with the egg. The other sperm joins
with the central cell. Angiosperms have double syngamy.
Also note: I am trying to get us to use syngamy rather
than "fertilization" as the latter has such diverse
meanings that are confusing in plant physiology, horti-
culture, etc. Fertilization leads us down several wrong
ideas about fertility, fertilizer, fertilized eggs,
and so on. Along these same lines I'm hoping we will
use zygote when we mean that.
ross
________________________________________________________________
Ross Koning | koning at ecsu.ctstateu.edu
Biology Department | http://koning.ecsu.ctstateu.edu/
Eastern CT State University | phone: 860-465-5327
Willimantic, CT 06226 USA | fax: 860-465-4479
____________________________|___________________________________
Electronic services composed and served from •Macintosh hardware.
