SYEFEST Activity: Wings On Seeds

Hope College, 1994
Contributor: Kathy Winnett-Murray

Starter Question:What characteristics of maple seeds help them travel farther and why is this important?

Curriculum Objectives: For Michigan Essential Goals and Objectives for Science Education (K-12): Constructing New and Reflecting on Scientific Knowledge; Using Scientific Knowledge - Life Science: Organization of Living Things, Evolution, and Ecosystems

Ecology Themes: Scale; Interactions between Organisms and their Environment; Interactions between Organisms (Seed Dispersal).

Overview:

The vast majority of our familiar flowering plants form structures called fruits that protect the developing plant embryo (contained within the seed) and to help disperse the seeds to new locations. WHY is it important for seeds to move someplace else? It may be helpful to think about this question by considering what might happen to a seed if all of the seeds from a parent plant simply dropped and landed right under the parent. Would this be a good place to germinate and grow to maturity?

Most fruits are adapted for dispersing seeds AWAY from the parent plant, where the young plants will not encounter as much competition for nutrients, water, and sun as they would if they remained under the parent with hundreds or thousands of other young plants. In addition, seed predators (squirrels, mice, birds, ants) and pathogens (bacteria, viruses, fungi) may be more successful in locating and destroying seeds if they occur in large clumps.

The seeds of fleshy fruits such as those of cherries and blueberries are tasty to many animals and are well adapted for passing through an animal gut intact. Other fruits have hooks, spines, hairs, or sticky surfaces and adhere to the feathers or fur of animals that brush against them; thus, they are eventually transported to new locations. The most common means for dispersal used by native Michigan plants (especially trees) is wind dispersal. Most of us, at one time or another, have aided the wind dispersal of dandelions and are familiar with the hairlike structures on dandelion fruits that enhance the distance that dandelion seeds will travel.

Maples are common trees in our area that have wind-dispersed seeds. A maple fruit has winglike extensions. When the fruit drops, the wings cause it to spin sideways. How does the spinning increase dispersal efficiency? If the seed remains aloft for a longer period of time, chances are it will move further from the parent plant because it is more likely to be caught in air currents for a longer period of time.

• Maple trees that are dropping fruits/seeds.
  
• Something for each student group to measure distance with - either tape measures, or pieces of strings marked at 1 meter intervals.
  

1. Decide on a comparison. Perhaps your students will want to compare dispersal distance of small and large winged seeds from the same tree. Or perhaps you will want to compare the dispersal distance of different types of maple if more than one species is available on your schoolyard.
   
2. If you are using size as a dispersal factor, you and your students will need to determine how to measure size. Here are some suggestions: a. Younger children might collect a pile of maple fruits and then make two piles - large and small. b. More advanced students could measure the surface area of each seed to be tested by tracing outlines on graph paper (count squares method) OR some teachers may have access to computer graphics that will compute area from a traced outline. c. If you have a balance available, use the fruit weight as an estimator of size.
   
3. Once the children have arranged their maple seeds into groups to be compared, the basic method is for the students to drop one seed at a time from any pre-determined height/location on the schoolyard that is at least 2 meters (about 6 feet).
   
4. For each seed dropped, record EITHER the distance travelled from the drop site OR the time aloft (the number of seconds it takes the seed to hit the ground from the time it is dropped). NOTE: If you measure distance AND time aloft, you will be able to have advanced students test the assumption that these two things are actually correlated - that is, does longer time aloft REALLY mean the seed goes further, on average?
   
5. Dropping fruits from greater heights gives more dramatic results! Second floor windows and stairwells might be exciting and good indoor possibilities for rainy days. Outdoor playgrounds often include some vantage drop sites!
   
6. Your results should be discussed in relation to plant survival and reproduction. Of all those maple seeds, the vast majority will never germinate. (Why not?) Of the seeds that germinate, the vast majority will never become mature trees (why not?) What are the consequences of fruit/wing design to the dispersal of the seeds? How is this related to plant survival and reproduction?

Here are some suggestions for related activities:

• What is the effect of wind speed on distance seeds travel.
  
• What is the effect of drop height on distance travelled?
  
• Compare different species of maple fruits - all have different characterisitc shapes and sizes and usually more than one are present in the neighborhood.
  
• Do big seeds come in big fruits and little seeds in little fruits, or not?
  
• Look for evidence of seed predators (munched seeds!) Do seed predators prefer big or little fruits? Certain species more than others? Measure the distance from the parent tree where each seed is collected and find out if more seeds are munched close to the parent tree or further out.
  
• Find out how many seeds have fallen various distances from the parent tree and construct a graph showing how many seeds are dispersed out to various distances. A typical graph would have many seeds close to the parent and fewer and fewer seeds as you go further and further away. The only problem with this is you run into seeds from other trees that look the same if you have lots of maples of the same species on the schoolyard, so try to pick an isolated tree.