For Seeds, Success Means Striking Out on Their Own

John Roach
for National Geographic News
July 16, 2004

If seeds could talk, they might sound like recent high school graduates making a beeline for jobs and colleges as far away from their parents as possible: "See ya 'rents, we're outta here."

Several studies have shown that seeds that stick too close to home have to put up with their parent's diseases and fight with the whole family for access to life's essentials: light, water, and nutrients.

Homebody seeds are also easier targets for predators. And some plants—like those that specialize in colonizing forest gaps or regenerating fire-ravaged landscapes—can only find fertile ground away from home.

Life, at least for a seed, is better out in the world.

"In general, seed dispersal away from the parent plant increases the chances that a seed will reach maturity," said Chris Birkinshaw, a biologist with Missouri Botanical Garden in St. Louis.

Seeds Get Around

Seeds know how to get around. Some fly with the wind, others go with the flow. Many hitch a ride with unsuspecting critters. But they all have the same goal: to take root and give rise to the next generation.

Scientists can understand what type of dispersal strategy a plant employs by looking at its environment. For example, dispersal by sea currents is important for plants that grow on seashores, wind is important in open grasslands.

And for each type of dispersal, there is a type of design. Wind-dispersed seeds are generally lightweight and have adaptations such as wings and parachutes so they can catch a ride on the breeze.

Water-dispersed seeds, such as coconuts, are buoyant. Seeds dispersed by animals usually offer a nutritional reward so that they are eaten, or they are sticky or barbed so they can latch on to passing bodies.

"Among species with seeds dispersed internally by animals, the size of the seed or fruit, its color, and the presence of protective adaptations—for example, the husk—will reflect the swallowing, visual, and processing abilities of the seed disperser," Birkinshaw said.

Continued on Next Page >>


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