The key to gene exchange between multicellular
individuals is haploid sex cells, each with just half
the adult DNA. They form gametes, sex cells that can
fuse with an opposite type. Ours are called eggs and
sperm. In the sea, haploid gametes produced by adults
simply float away. Nearly all are quickly eaten, so it’s
all a numbers game. When male and female gametes
meet by chance, a tiny embryo begins to grow.
Deep in the Carboniferous Era, 300 million years ago,
vast swamps, bogs, and soupy bays teemed with life.
Tall spreading tree-ferns, newt-like amphibians the
size of crocodiles, and dragonflies bigger than gulls
released gametes into the water as their ocean ances-
tors had done. Some gametes fused and grew, creating
babies. These days, fish, frogs, and some water plants
still do it that way.
Plants began to colonize in a far harsher environment
about 270 million years ago with multiple challenges
to reproduction. Dry land offered huge opportunities
for those who could survive its rigors—but, how were
they going to get those haploid cells to meet up?
LAND PLANTS GET IT DONE
Evolution is infinitely creative, given enough time.
The simplest solution for plants was to let the wind
carry away lightweight haploid cells—aka pollen—
that just might find a female sex cell clinging to a twig
or bract somewhere. The gymnosperms (“naked seed”
in Greek), including primitive gingkoes and cycads,
plus pines, firs, and their relatives, were the first to
use the wind to carry pollen on a massive scale.
Many flowering plants still make use of air transport.
Grasses produce tiny dangling flowers that wait for
a warm, dry day to release vast numbers of pollen
grains, as hay fever sufferers will confirm. But wind
is chancy. And it’s not efficient in damp climates or
sheltered locales.
Most of the flowering plants we see address the risks
of chance with a more surefire solution. They invite an
animal partner, most often an insect, to help fertilize
the embryo. In fact, the whole reproductive purpose
of lush and lovely flowers is to attract these willing
workers in the plant sex game.
The pollinator visits the beckoning flower seeking
nectar, inadvertently touching a male stamen covered
with sticky pollen, then carries it to the next flower.
With luck, a grain sticks to a female stigma atop a tall
pistil in a flower of the same species. There, it sends
down a tube through which new genes reach the ovule
below. Around the growing seed, the ovary may swell
to become a succulent fruit or berry, inviting another
animal to enjoy a meal, carry away indigestible seeds,
and defecate them in a new spot. Of course, manure
helps young plants thrive.
“
THE WHOLE
reproductive
purpose of lush and
lovely flowers is to
attract these willing
workers in the
plant sex game.”
grow cycle
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