Forest Preserve District of Cook County, Illinois
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Dispersal
Nature Bulletin No. 675-A   April 15, 1978
Forest Preserve District of Cook County
George W. Dunne, President
Roland F. Eisenbeis, Supt. of Conservation

SEED DISPERSAL
Plants that scatter their seeds widely have a better chance to survive than those which do not. Different kinds spread their seeds in various special ways.

Many seeds ride the wind. Maple seeds spin away like little helicopters with a single wing. In a strong breeze they can travel a city block. Those of the elm are small papery disks with a seed in the center. The ash seed and its wing resembles a canoe paddle. In the basswood a few seeds are suspended beneath a large flat blade that glides through the air. Ripe, dry pine cones open and release winged seeds hidden between the cone scales.

The wisps of cottony fuzz that we see drifting about in spring carry the tiny seeds of willow, cottonwood and aspen. In a high wind they travel for miles. The dangling seed balls of the sycamore break up into hundreds of parachutes of fine fibers each supporting a single seed. The dandelion, cattail, thistle and milkweed also launch parachutes into the wind.

When its seeds are ripe, the stem of a tumbleweed breaks off at the surface of the soil. In a strong wind this large bushy plant goes rolling and bumping across fields and open country scattering seeds at every bounce.

The coconut palm thrives on the coasts of tropical seas. Its nut, the largest of all seeds has a protective, waterproof covering which allows it to float to a far-distant beach, germinate, and grow a new tree. Dozen of our Illinois plants on shorelines and floodplains are spread by floating seeds. The silver maple, giant ragweed, lotus pods with their seeds, and native pecans, are examples.

Several common plants in our forest preserves "shoot" their seeds, sometimes for many feet. The ripe seed pods of the violet explode. When gently touched, the slender capsule of the jewelweed or touch- me-not snaps into five tight coils throwing seeds in all directions. As the nut-like pod of the witchhazel tree slowly dries and shrinks, the pressure forces its two seeds to pop out. Each seed of the jumpseed -- one of the smartweeds -- has a short stem with a core of compressed pith that shoots the seed like a popgun when jostled.

Many kinds of sweet, pulpy fruits and berries, such as raspberries, gooseberries, elderberries, grapes, red haws and cherries are eaten by birds and other animals. The soft parts of the fruit are digested, but the seeds are able to pass through the intestines undamaged and be dropped, often long distances away.

Gray squirrels and fox squirrels bury oak acorns and the nuts of hickory and walnut for winter food. Some are carried considerable distances away, forgotten, and start new trees. In this way uncultivated fields are slowly being reforested from nearby woodlands.

The burs are "hitch-hikers, " seeds equipped with hooks or barbed spines that cling to our clothes and to the hair or fur of animals. Burs are of many types. Sticktights are the bean-like pods of the legume, tick trefoil. Spanish needles are shaped like pitchforks. The sandbur, with its stiff, barbed spines, stabs into the feet of dogs and barefoot youngsters. Burdock, cocklebur, beggar's lice and bedstraw are other common seeds that steal rides.

Accidentally, or carelessly, the seeds of many undesirable plants were brought across the ocean in ships and allowed to escape and grow. Almost all of the most troublesome weeds in our farms and gardens are newcomers to America.


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