Sock Seeds

Resource for Grades K-8

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Video

Running Time: 3m 00s
Size: 8.9 MB

Source: ZOOM

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Sock Seeds (Audio Description) (Video)

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Background Essay

Millions of years of evolution have shaped the form and function of plants. One of the most effective evolutionary strategies of plants is seed dispersal, or the scattering of offspring (seeds) far away from the parent plant to a potentially better growing environment. Seed dispersal enables an essentially immobile organism to "move" its offspring to a new location. Doing so prevents the offspring from having to compete with the parent plant for light, water, and nutrients, thus giving the offspring a better chance for survival.

Wind and water are probably the two most effective transport systems used by plants to disperse their seeds. A single gust of wind can carry hundreds of thousands of dandelion seeds from one field to the next. Similarly, ocean currents can transport plants thousands of miles, from one continent to another. Some plants, however, use animals to transport their seeds to new locations. Berries, for example, entice animals to ingest seeds and later distribute them, undigested, in another location. Other seeds have hooks, barbs, and burs on their surfaces that can attach to an animal's hair or fur like Velcro®. These types of seeds, called "hitchhikers," are the most likely to attach to your clothing as you walk across your yard, a field, or through the woods.

Like many traits that prove to be advantageous to an organism, the structures on seeds that allow them to hitchhike on an animal's fur probably began as a fortunate accident. Perhaps one individual plant had a mutation that resulted in small, hook-shaped projections on its seeds. These otherwise functionless structures may have allowed some of that plant's seeds to attach briefly to passing animals and thus travel farther afield and do better than the seeds of other plants of the same species. Gradually, over thousands of plant generations, if the advantage of hitchhiking was great enough, plants with the stickiest or prickliest seeds would have outcompeted other plants of the same species and done a better job of passing their seed form on to future generations.

So the next time cockleburs stick to your socks or sandburs flatten your bicycle tires, you might feel a little less annoyed if you think of them as a magnificent evolutionary strategy instead of a bunch of pesky weed seeds.

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Discussion Questions

Why is it best to do this activity in the late summer or fall?

Why is it best to do this activity on a sunny day?

What enables the seeds to stick to the sock?

Do some seeds stick better than others? Why?

How do you think the ability to stick "helps" the plant?

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Transcript

(bubbling)

RACHEL: Check out our garden. Do you know how we grew it? By planting a sock. Weird, huh? Well, it's not just an ordinary sock. It's a sock that was worn out in a field, outside in the country.

ESTUARDO: Joshua T. of Venus, Texas, told us how to use socks to grow plants. It's a great way to find out what kind of plants grow in different biomes. Joshua says the best time to do this is on a sunny day in late summer or early fall.

RACHEL: First, find an old, fuzzy, worn-out sock that can fit over your shoe. Then go wandering around outside. You can do this in the city or in the country, and you can go walking around in the woods or in a lot that has some weeds. Then walk back and forth in an area that's growing some plants.

ESTUARDO: Take off your sock and examine the kinds of seeds stuck to it.

RACHEL: Oh, cool.

ESTUARDO: This looks like a wheat seed.

RACHEL: And over there there's an orange seed.

ESTUARDO: And those ones are dark brown. They're different colors.

RACHEL: Now, to plant your sock, you're going to take a shoe box and line it with a garbage bag or plastic wrap, like this. Then you're going to put some potting soil into your shoe box so that it covers the bottom. Okay.

ESTUARDO: Now cut a slit down the side of your sock. I have one that's already cut, see? And now I'm going to unroll it so I can cut the part that doesn't have any seeds on it. There we go. All right, almost done. There, cool.

RACHEL: Now, take your sock and flatten it out so that it goes into the bottom of your box, like that. And make sure the seeds are facing upwards. Then put a thin layer of potting soil on the top of your sock. So I'm just going to cover it. Good.

ESTUARDO: That's cool. Just sort of...

RACHEL: Yeah, make sure it spreads out.

ESTUARDO: Yeah, spread it out.

RACHEL: I just want to make sure I get all of it.

ESTUARDO: Yeah.

RACHEL: Okay, that's good. Then water your sock. (both laughing) Okay, that looks good.

ESTUARDO: There we go.

RACHEL: In a week or so, your seeds should begin to sprout and look like this.

ESTUARDO: Oh, that's awesome. This is really fun to do in different environments, because you get different results every time. I wore the sock that's in this shoe box outside on my lawn. That's in the city.

RACHEL: The sock that was planted in this box was worn in a field of wildflowers in the suburbs. Isn't it pretty?

ESTUARDO: Oh... it's so...

RACHEL: Soft.

ESTUARDO:I know, it's sort of fuzzy, too.