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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 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 thrive.
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 deep.

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 years.

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.