This Week's Experiment - #282 Seed Search
The idea for this week's experiment came while walking our new dog, Bryn. He
is a seven month old Lab/Chow mix and is quite a handful. While walking, he
often gets seeds or burrs in his fur. Now why would plants make burrs just
to bother my dog (and me)? To find out, you will need:
an area with some weeds
some long pants
some cherries, plums, apples or other fruit with hard seeds
First, look carefully at the weeds. Make sure that they don't contain any
wasps, bees, snakes, lions or, tigers or bears, oh my. Once you are sure you
will not disturb the local wildlife, walk through the weeds. Then carefully
examine the legs of your pants. Depending on the time of year and the kinds
of weeds in your area, there is a very good chance that you will find some
burrs stuck to the cloth. Look at them carefully.
The burrs that you found are actually seeds, intended to grow new plants.
One problem that plants face is that they can't walk around. If a cherry
tree could go for a walk, then it could drop its seeds here and there along
the way, spreading cherry trees across the country. Since the tree is
rooted in one spot, it needs another way to spread its seeds. Try eating a
cherry. Eat it carefully, because in the center you will find a large, hard
pit. That pit is actually a cherry seed. When you finished eating the
cherry, what did you do with the pit? You threw it away, right? Animals do
the same thing. A bird could carry the cherry to a nearby fence. After
eating the cherry, it drops the pit, planting a new cherry tree. If the bird
swallows the pit, it will eventually pass on through the bird and still have
a chance to grow into a tree. Some plants have seeds that can only grow when
they have passed through a bird.
Burrs are another way that plants can spread their seeds. Instead of
offering a yummy treat as the bribe for carrying a seed, plants with burrs
bother you into planting their seeds. Here in St Augustine, we have a plant
called a sandspur. The plant looks like an ordinary clump of grass, but it
produces clusters of VERY sharp, thorny seeds. These things really hurt!
While walking on the path to the beach, you can see tourists step on one.
They yelp, hop on one foot, and say all sorts of naughty things as they pull
the thorny seed out of their foot. Then they do something that they really
should not. They throw the seed on the ground! They have just planted
another sandspur plant!
Some burrs just stick to you instead of hurting. If you are lucky enough to
have some of these, look at them very closely. You may want to use a
magnifying glass or microscope. Look carefully at the hook-like hairs. Do
they remind you of anything? Next, look carefully at some Velcro. Wow, it
looks the same. It should. Plant burrs gave George de Mestral the idea for
Velcro.
There are many other ways that plants spread their seeds. Wind is a great
way for plants to spread. The next time you blow the seeds from a dandelion,
remember that you have just planted quite a few more weeds in your lawn.
Plants like Jewelweed have seed pods that build up tension as they ripen.
When the seed is ready, the slightest touch causes the seed pod to split
apart, throwing seeds in all directions. Some seeds float in water, letting
the current move them to new locations.
Of all the different ways, I think I like the cherries the best. In fact, I
think I will go prepare some cherry seeds right now. Have a good week.
From Robert Krampf's Science Education Company
PO Box 60982
Jacksonville, FL 32236-0982
904-388-6381
krampf@aol.com
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