A Seedy Story
A seed can be a mere .0078 of an inch long. Or a seed can
be a foot long, eight inches thick and weigh 40 pounds. While
there's not much physical resemblance between the tiny witchweed
seed and the double-coconut, their reason for being is identical...to
establish the species in a new location. The methods seeds use
to reach new locations are as diverse as the seeds themselves.
Anyone who has witnessed a blizzard of fluff swirling through
the air on a windy autumn day won't be surprised to learn that
wind dispersal is the most common means of seed distribution.
The dandelion, Canada thistle and fireweed all have tufts or
plumes many times the size of the actual seed. When ripe, the
seeds break away from the parent plant and "sail through
the air with the greatest of ease." They rise and fall with
the wind, even rise again from the ground. Before the seed finally
comes to rest, it may travel hundreds of miles.
Another class of
airborne seeds are those with wings. Maple, ash and basswood
are among the best known in this category. Although they make
out well enough to ensure that these trees survive, the seeds
do not have the same mastery of the air as the tufted types and
travel much shorter distances.
Other plants rely on cunning to get around. They either entice
or trick animals, including the two-legged variety, to act as
a carrier for their seeds. Some offer the reward of food. The
flesh on a fruit is intended to whet the appetite of a passing
animal. But either the seed itself is too large and hard to be
eaten and is spit out, or the seed has a protective coating that
enables it to pass through a digestive tract unharmed.
The oak tree carries things one step further. In co-operation
with squirrels, it has its acorns buried under ideal germinating
conditions. Just how many the squirrel an find again nobody seems
to know for certain, but enough are forgotten that oak trees
So much for the plants that use bribery. Now for the ones that
are downright sneaky, the ticks and burs. Get these plants within
grabbing distance of a passerby's coat - be it fur, feather or
cloth - and they'll hook right on, probably undetected. And there
they'll stay until forcibly removed.
Sometimes, the fish below and the birds above team up to move
seeds further than would normally be expected. There are documented
cases of a fish eating yellow water lily seeds, of a heron eating
the fish, and the seeds being excreted many miles away in another
body of water.
The way in which a particular plant goes about distributing
its seeds is an important factor in determining where that plant
will grow. One of the reasons thistles, dandelions and similar
plants occur in abundance along fences, hedges and buildings
is that when the wind is deflected by these objects, some of
the seeds being carried along by the wind drop to the ground.
Oak trees tend to grow in clumps, partly because squirrels normally
carry acorns only a short distance before burying them.
With all those plants making and distributing all those seeds,
an awful lot of seeds find their way into the ground. One investigator,
who must have had a lot of patience, recorded from 10,000 to
30,000 viable seeds in patches of soil a yard square and 10 inches
Which raises another question. How long does a seed in the
soil remain viable - for how long is it capable of playing the
waiting game until conditions become right for germination? A
heck of a long time. It used to be generally believed that 150
years was about as long as a seed could survive in the soil.
However, carbon testing has dated some seeds at between 850 and
1,250 years old. These seeds, when given favourable conditions,
germinated. This, of course, is an extreme case, but it's not
at all unusual for seeds to remain viable in the soil for 20
A dry seed is so well protected that it can tolerate deep
freeze conditions for years without loss of vigor. In fact, most
seeds in northern climates require a period of deep freeze before
they'll germinate. That's what keeps seeds scattered in the autumn
from germinating the same year and being killed by winter before
they have a chance to produce seeds.