World Builders™
World Builders™
Session Eight --  Land Plants  
Session Eight  -- Land Plants  
 



How Seeds Travel
How Seeds Travel

 

    Plants are rooted in one spot, but seeds are great travelers. Over the millennia plants have found many ways to travel as seeds. They have found ways to make use of natural forces, such as water and wind. They have also learned to travel with animals and birds.

    The seeds of land plants vary widely in size and shape. These seeds are made up of two elements:

  • a tiny dormant cell that can divide to form a new plant and
  • a food supply that the young plant can draw on as it begins to grow

Angiosperm seeds also have a seed coat, which is a protective covering.

To these two essential elements, some plants added small thorns to make seeds sticky or an outer covering of fruit that would attract animals that would carry the seeds away.

Using Animal Power

     Some flowering plants package their seeds in fruits and berries. Many small berries keep well on the branches and become food for birds in winter. The small seeds are hidden in the berry pulp. The birds swallow the berries whole and the seeds pass through their digestive tracts. The birds fly and the seeds fly free! Birds often transport small seeds in this way.

     Some plants produce large, sweet, perishable fruits. These fruits are fragrant, and attract tree climbers, like raccoons, as well as grazing animals. In carrying away the fruits, the animals also carry away the seeds. In the wild these fruits are smaller than the ones that humans have selected to grow in their orchards.

     Other plants produce nuts: seeds with hard shells. These seeds roll and bounce, and are gathered by small animals, like squirrels.

     Here is another way that plants use the animals that feed on them.

Hitching Rides

     Many low-growing plants grow seeds that are sticky, or that have little hooks on them. These burrs stick to the fur of passing animals (and the clothing of passing humans) and are carried away to grow in new places.


     The relationships between animals and plants demonstrate how an ecosystem works. A biome is not a collection of individual life forms all "doing their thing". Living things live together in communities, and in these communities the different species give and receive in mutually beneficial exchanges. Plants put some of the energy that they capture into making fruit. The animals eat the fruit and scatter the seeds. Both plants and animals benefit.

Using Wind Power

     Some plants equip their seeds to fly with the wind. Dandelion seeds floating in the air are good examples of this. Their seeds are attached to a thin stem which has a fluffy parachute-like top.

     In this picture you can see the fluffy ball of tiny parachute tops.  The seeds are inside these balls and they rest on the tops of the stems.

     A passerby who brushes against these ball of fluff, or even a good puff of wind, can free the seeds to float away and find a place where they may germinate.

Cottonwood seeds and milkweed seeds also float in clouds of fluff. On a windy day, floating seeds can be blown for miles.

    Other seeds let the wind spin them by growing propeller-like vanes. Maple seeds have this shape. While this shape probably does not move the seeds very far from the parent tree, it does bring the seeds down with a twirling motion. As they land in the litter of fallen leaves, that twirling may help them to dig in deeper, closer to the ground.

Water Power

      Some plants use moving water to scatter their seeds. One terrestrial plant that does this is the coconut tree . Coconut trees are flexible and bend a long way in the wind. During a storm coconuts may fall onto the beach or into the ocean. They float from one island to another and get washed up on the beaches, where the seeds sprout and become new trees.


Photographs from a Corel CD-ROM : for viewing only, not for downloading.   More Information.
Dandelions by Viau

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Copyright © 1999, 2003, 2005.   Elizabeth Anne Viau and her licensors.  All rights reserved. This material may be used by individuals for instructional purposes but not sold. Please inform the author if you use it at eviau@earthlink.net