|
This week's LabZone activity
May 12, 2004
Traveling Plants
Like many naturalists, Darwin wondered how plants migrated to isolated islands. A plant native to one country might also be discovered growing naturally on an island hundreds or even thousands of miles away, even though it was not brought there by humans. Darwin guessed that some seeds floated across the ocean from one place to the next, either on their own or stuck in pieces of driftwood. Darwin was the first person to do experiments to see if seeds could stay in seawater for a long time and still be able to sprout. He proved that even though most plants cannot survive in a salty environment for long, some seeds can float across the ocean and still sprout into plants. This is a smaller version of Darwin's experiment.
What you need
- a cup or bowl
- salt
- various kinds of seeds (good ones to use are peas, cucumber seeds, radish seeds, beans, or asparagus seeds)
- several small plant pots, or empty yogurt containers with holes poked in the bottoms
- soil
Fill a cup or bowl with water, and sprinkle in enough salt until the water tastes noticeably salty—about one teaspoon (5 ml) per cup (240 ml). Drop two or three of each kind of seed into the water. Some might float; some might sink. Let the seeds soak in the saltwater for two days, as if they were floating in seawater on their way to an island that is a two-day journey away.
Fill your small plant pots (or yogurt containers) most of the way with soil, and pat it down. After the seeds have been in the water for two days, plant one seed in each pot, making sure to create labels showing which kind of seed is in which pot. Push each seed about a quarter inch (6 mm) below the soil level and smooth it over. Place the pots in a sunny location, preferably on a tray or dish.
Water the seeds thoroughly at first, and every day sprinkle a little water to keep the soil moist (but not soggy). Wait for the seeds to sprout. It can take anywhere from two days to two weeks, depending on the type of seed; check the seed packets.
How many of the seeds sprouted? All? None? Some? Did the salt poison them?
It would only take a single seed floating to an island and successfully sprouting to establish that new kind of plant on the island, since the plant would then mature and drop seeds of its own.
Activity excerpted by permission of Independent Publishers Group from Darwin and Evolution for Kids: His Life and Ideas, with 21 Activities by Kristan Lawson. Published by Chicago Review Press, distributed by Independent Publishers Group (www.ipgbook.com). Text copyright © 2003 by Kristan Lawson.
Talk Back:
Do you have any comments about this activity? Send them
to us using the form below.
|
SNK RSS Feed 
