Nature Nugget – Seed Dispersal Methods

An important function of seeds is dispersal, a method of establishing new plants in suitable places away from the parent plant so as to avoid competition with it. There are three main methods of seed dispersal: hitchhiking with animals and humans, drifting on ocean or fresh water, and being carried by the wind.

Some common hitchhiking seeds include the cocklebur and the seeds of the burdock plant which attach like Velcro to fur and clothing. Other hitchhikers go by such names as beggar-ticks, sand-burs, stick-tights, and grappling-hooks. Some seeds hitchhike on the inside of animals and humans by being eaten and passed unharmed through their digestive tracts and finally being deposited on the outside with fertilizer a day or two later. A good example of this is the persimmon seed which is commonly seen in the droppings of raccoons and opossums. Some seeds even require the scarification they receive when passing through the gizzard of birds, before they will germinate and grow. An example of this is the tough seeds of the American lotus, a type of lily pad, which is eaten by waterfowl and carried from one lake to another. The seed coat of this plant is so tough that it actually has to be eaten several times before it is scarified enough to germinate.

Drift seeds can drift on ocean currents for thousands of miles before being deposited on the shores of a distant continent or remote tropical island. Their thick shells protect them from saltwater, allowing them to survive months and even years at sea. Some common drift seeds are the coconut, nickernut, sea bean, sea heart, box fruit, and beach morning glory. The acorn of the burr oak is an example of a freshwater drift seed. A thick, corky cap covers most of the acorn, which gives it good flotation. Rising floodwaters carry it downstream and across floodplains to be deposited when the waters recede. Back currents on the floodplain can even carry it upstream from the parent tree.

Hundreds of seed species in many plant families use the remarkable method of wind dispersal, including many we know as weeds. A lot of weedy composites, such as the European dandelion, have worldwide distributions, because their seeds can be carried vast distances by the wind. Some adaptations for the wind dispersal method include seeds that resemble parachutes, helicopters, and gliders. Parachute type seeds have a plumose crown of hairs, some shaped like an umbrella, above the slender seeds. They are so fragile that they can become airborne with the slightest breeze and can literally soar over mountains. Common examples of this method of seed dispersal include salsify, dandelions, milkweeds, thistles, and many types of sunflowers. Helicopter type seeds have a single, rigid wing at one end. The wing has a slight pitch, causing the seed to spin as it falls. Depending on height above ground and wind velocity, helicopter seeds can be carried a considerable distance. Common examples of plants with helicopter seeds are maples, ashes, pines, spruces, firs, and hemlocks. Glider type seeds have two papery lateral wings that resemble an airplane. When released from the tree they sail through the air like a glider. An excellent example of this method is the seed of the tropical Asian climbing gourd. The seed has a five-inch wingspan that resembles a “flying wing” aircraft, such as the Stealth Bomber, and glides through the air of the rain forest in wide circles.

Just as these seeds are carried and dispersed all over by wind, water, and hitchhiking, so should the gospel seed be dispersed and scattered all over the world by Christ’s followers. “Present truth should be scattered among the people like the leaves of autumn.” Evangelism, 36. “Now is the time to sow the gospel seed. . . . We have no time to lose.” Counsels to Parents, Teachers, and Students, 250.

David Arbour writes from his home in DeQueen, Arkansas. He may be contacted by e-mail at: landmarks@stepstolife.org.