Silverhill Seeds: Seeds from Africa€¦ · Silverhill Seeds: Seeds from Africa
[email protected] how do seeds travel?
4
[email protected] HOW DO SEEDS TRAVEL? SLIDE SHOW SCRIPT prepared by Richard Carstensen for Discovery Southeast Original 1990, updated 2007 Note to Discovery naturalists and teachers I used these slides in my third and fourth grade Nature Studies program at Harborview in the early 1990s. The script however is written at a high school level, to provide you with precise information should you need it. Middle and grade school teachers can easily adapt the script for their students by replacing the italicized technical words with the simpler words offered in parentheses. You may wish to present some of the technical words in a separate class before viewing the slides. At Harborview I prefaced this slide show with a discussion of possibilities for seed dispersal. Most strategies are intuitively obvious, and can be elicited from the class just by asking the right questions, like: How might a seed be shaped so that it could hitch- hike a ride in an animal’s fur or feathers?, Or: How could a seed travel inside an animal and still survive? (Be prepared for giggles and horrified locks when you ask this one. I plan an extra several minutes to let hysteria and wisecracks run their course before proceeding. This paves the way for more casual discussions when we get into scat in our winter tracking classes.) The very last slide requires familiarity with the use of tables, and a fairly advanced logical facility. I don’t use it in third grade, and even in fourth grade when we examine seed dispersal strategies in the context of our different natural communities, teachers report a wide range in comprehension of the table. It’s probably most appropriate for middle and high school classes. In third and fourth grade I don’t get too technical about what a seed actually is. In fact I don’t distinguish between seeds and spores. But you may wish to begin your discussion with these basic definitions. A seed is the fertilized ovule of the ‘higher” or flowering plants, composed of an embryo with a food supply. A spore is like a seed but consists of a reproductive cell (usually a single cell), lacking a food supply, and found In the ‘lower plants like mosses and ferns, and in the fungi (eg. mushrooms). Spores tend to be smaller than most seeds. 1) Title slide e illustration on this opening slide is of 2 Sitka spruce cones, showing the size range. Bracts covering the seeds are shown above, with the winged seed itself in the center. 2) Dispersal illustration Wind ere are at least 3 ways that a seed can take advantage of the wind. One is to have a wing, like the spruce seed. Another is to have a fuzzy, or plumed seed, like dwarf fireweed. And many plants have such tiny seeds that they need no attached wings or hairs to float about in the air. Wintergreen is one such flowering plant. Tiny spores (see above definitions) of mushrooms, mosses and ferns also are moved about in the air. Water Most plants which live partly or entirely in the water have seeds which float. ey can be moved about on the currents. “Unspecialized?” It’s pretty hard to imagine how the seed of a plant like beach pea gets around. It must have some tricks we don’t yet understand! Animals Seeds can use animals either by hitch- hiking a ride on their fur or feathers, or by being eaten, and somehow not being digested, but surviving in their scat. 3) Dwarf fireweed seed Dwarf fireweed and its cousin tall fireweed have plumes attached to their seeds which allow them to travel for miles on breezes. is slide shows an area about one centimeter across -- the scale is in millimeters. What other plants do you know which have plumed or fuzzy seeds? (Answers Dandelion, willow, cottonwood.) 4) Licorice fern e sori (small paired dots) on the underside of this licorice fern each contain thousands of spores, too small to see, so tiny they easily float in the air. To get an idea of the size of these spores, let’s zoom in on a few of the sori.
Transcript of [email protected] how do seeds travel?
how do seeds travel?slide show script
prepared by Richard Carstensen for Discovery SoutheastOriginal 1990, updated 2007
Note to discovery naturalists and teachers I used these slides in my third and fourth grade Nature
Studies program at Harborview in the early 1990s. The script however is written at a high school level, to provide you with precise information should you need it. Middle and grade school teachers can easily adapt the script for their students by replacing the italicized technical words with the simpler words offered in parentheses. You may wish to present some of the technical words in a separate class before viewing the slides.
At Harborview I prefaced this slide show with a discussion of possibilities for seed dispersal. Most strategies are intuitively obvious, and can be elicited from the class just by asking the right questions, like: How might a seed be shaped so that it could hitch-hike a ride in an animal’s fur or feathers?,
Or: How could a seed travel inside an animal and still survive? (Be prepared for giggles and horrified locks when you ask this one. I plan an extra several minutes to let hysteria and wisecracks run their course before proceeding. This paves the way for more casual discussions when we get into scat in our winter tracking classes.)
The very last slide requires familiarity with the use of tables, and a fairly advanced logical facility. I don’t use it in third grade, and even in fourth grade when we examine seed dispersal strategies in the context of our different natural communities, teachers report a wide range in comprehension of the table. It’s probably most appropriate for middle and high school classes.
In third and fourth grade I don’t get too technical about what a seed actually is. In fact I don’t distinguish between seeds and spores. But you may wish to begin your discussion with these basic definitions. A seed is the fertilized ovule of the ‘higher” or flowering plants, composed of an embryo with a food supply. A spore is like a seed but consists of a reproductive cell (usually a single cell), lacking a food supply, and found In the ‘lower plants like mosses and ferns, and in the fungi (eg. mushrooms). Spores tend to be smaller than most seeds.
1) title slide The illustration on this opening slide is of 2 Sitka spruce cones, showing the size range. Bracts covering the seeds are shown above, with the winged seed itself in the center. 2) dispersal illustration Wind There are at least 3 ways that a seed can take advantage of the wind. One is to have a wing, like the spruce seed. Another is to have a fuzzy, or plumed seed, like dwarf fireweed. And many plants have such tiny seeds that they need no attached wings or hairs to float about in the air. Wintergreen is one such flowering
plant. Tiny spores (see above definitions) of mushrooms, mosses and ferns also are moved about in the air.
Water Most plants which live partly or entirely in the water have seeds which float. They can be moved about on the currents.
“Unspecialized?” It’s pretty hard to imagine how the seed of a plant like beach pea gets around. It must have some tricks we don’t yet understand!
Animals Seeds can use animals either by hitch-hiking a ride on their fur or feathers, or by being eaten, and somehow not being digested, but surviving in their scat. 3) Dwarf fireweed seed Dwarf fireweed and its cousin tall fireweed have plumes attached to their seeds which allow them to travel for miles on breezes. This slide shows an area about one centimeter across -- the scale is in millimeters. What other plants do you know which have plumed or fuzzy seeds? (Answers Dandelion, willow, cottonwood.) 4) licorice fern The sori (small paired dots) on the underside of this licorice fern each contain thousands of spores, too small to see, so tiny they easily float in the air. To get an idea of the size of these spores, let’s zoom in on a few of the sori.
5) closeup This entire slide shows an area only about one centimeter across. These 8 sori each contain about fifty little spore packets. The packets themselves contain hundreds of spores, and will soon split open to release them. 6) alder, spruce and hemlock “cones” Several of our trees have winged seeds, borne inside cones. Winged seeds can’t travel so far as plumed or fuzzy seeds, so perhaps it makes sense that they’re found on trees that can release them from high in the air where they get a “head start.”
The pair of cone-like fruits in the upper left are from an alder. In the upper right is a spruce cone. The hemlock cone at bottom is shown in different stages of opening. As the scales spread apart on dry days the winged seeds fall out, and spin rapidly, which can sometimes carry them hundreds of feet from the parent tree. The next slide shows seeds of these 3 trees, in the same positions as the cones in this view. 7) closeup of seeds Alder seed has 2 wings, spruce and hemlock seed each have just one. Alder seed is the lightest, and can carry the farthest on the wind. 8) Goosetongue Most of the plants that grow in our salt marshes (intertidal wetlands) have floating seeds. Here is the delicious goosetongue, at high tide, with its seed heads about to be submerged.
9) seeds at high tide line Seed of salt marsh plants drifts up to the high tide mark and often is deposited in huge piles. This is one of the many features that makes the drift or debris zone so attractive to birds and mammals. The seeds in this photo are of Lyngbye sedge, a salt-tolerant grass-like plant that produces bushels of seeds in the fall. 10) pondweed Freshwater aquatic plants produce flowers and seed heads at the water surface, and when seeds are released they drift about on the surface. The floating seeds can also become attached to the plumage of waterfowl, and carried to distant ponds. Newly created ponds quickly become colonized by plants like the pondweed in this photo, brought in as seeds stuck to the feet and feathers of ducks. 11) Berries Here are 5 of our common berry-like fruits. Clockwise from the upper left they are: blueberry, strawberry, elderberry, twisted stalk (or watermelon berry) and devil’s club. One of each of the berries has been sectioned to show the seeds, although this isn’t necessary for strawberry, which bears its seeds on the surface of the fruit. A berry is costly for a plant to produce, and the whole purpose of berries is to be eaten. The juicy part of the fruit is digested, and the hard seeds are carried about and eventually excreted by animals. The following slide shows the seeds of these berries, arranged in the same positions. 12) closeup of seeds Clockwise from the upper left these are seeds of: blueberry, strawberry, elderberry, twisted stalk (or watermelon berry) and devil’s club. The 2 huge seeds
[email protected] �in each devil’s club berry occupy almost the entire fruit, and are not favored by people, but highly sought by bears and birds. Seeds in berries usually have hard coats that resist the digestive enzymes in animal’s stomachs, and even the powerful grinding action of grit- filled bird gizzards. Many can pass through the animal and survive in its scat. 13) Bear scat with soapberry seeds The comb in this picture is for scale. It’s 5 inches long. The darkened area in the center is where the mosses were killed the previous autumn by a bear scat. The scat was composed mostly of soapberries, which don’t grow near Juneau but are common in Glacier Bay and Haines. The pulp from these berries washed away long ago, but many of the large black seeds can still be seen. The small green sprouts clustered near the comb are baby soapberry plants, thriving in the nutrient-rich seed bed. 14) Forest seed cycle This collage shows several stages in the life cycle of a red huckleberry plant, and 2 of the animals–varied thrush and brown bear–that help move its seeds. In the lower left is a berry that was chewed by a deer mouse, revealing the seeds. Just above it is a first year sprout, only a few millimeters high. Sometimes hundreds of these sprouts germinate in a single bear scat, but only a few will survive to the creeping evergreen-leaved stage, shown in the lower right. And of these small evergreen huckleberries, only those receiving enough light will grow into fruiting bushes, like this one, shown in fall after the leaves have dropped. 15) vegetative spread Many plants can colonize new places without relying on seed reproduction. Bunchberry or ground dogwood has runners or underground stems that simply grow
into nearby habitats. Sometimes a large patch of bunchberry leaves is a single plant, connected by runners. Of course the seeds in bunchberry also are dispersed by birds like blue grouse, so the plant has more than one option for dispersal. What other plants colonize by runners? (Answers, strawberry, trailing raspberry, many grasses and sedges.) 16) sidewalk plantain Here is one of the few plants that survives in school yards and along sidewalks, highly resistant to trampling. It always seems to be found near human disturbance, and in fact it probably relies mostly on people to distribute its seeds. These are shown in the next slide.
17) plantain seeds The seeds of plantain when moistened develop a clear sticky coating or “glue” which adheres to shoes. Its easy to watch this by placing several seeds in a drop of water for about ten minutes, and then studying them with a hand lens. 18) hitchhikers Plant seed that catches on fur or feathers could be called hitchhiking seed. The seeds on this pile jacket are, clockwise from upper left: cotton sedge, large-leaved avens (with some of the individual seeds teased out and placed next to the seedhead), squirreltail grass and bedstraw. All have attachments that help the seed adhere to fuzzy surfaces. Cotton sedge is mostly carried by the wind, like willow and fireweed, but is also animal distributed. Avens has a tiny ‘fishhook’ on each seed, barely visible in this
photo. Squirreltail grass seed has a “spear” that often penetrates fur or clothing, and bedstraw seeds resemble little velcro balls. Hitchhiking seeds are found mostly in our meadow, or early successional communities, and are relatively uncommon in forest habitats. 19) seeds and pods of meadow plants These seeds may have sophisticated dispersal strategies, but we haven’t figured them out yet. Far from being designed for easy wind dispersal, they might be described as “bomb seeds”. Clockwise from upper left: lupine, yellow rattle, black lily, beach pea and iris. In some cases heavy round seeds may be needed to penetrate the meadow’s moss layer, in order to reach mineral soil where they can germinate. A large heavy seed can also carry more food to get the seed started. This is important because the sprout may need to grow several inches tall before it emerges from the moss into the sunlight, where it can begin producing its own food through photosynthesis. 20) communities table Do seed dispersal strategies differ in our different natural communities? Sure! For example, notice on this chart how many berry-producing plants grow in the old-growth forest. What other patterns do you notice on this table? Would you expect more plants to rely on wind distribution in the forest or in open habitats like meadows? Should plants with winged seeds be taller than the other species in their community?
