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With and Without: Is Light on the Soil Needed for Mustard Seed Germination?

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Author: Janice VanCleave

Problem

Is light on the soil needed for mustard seed germination?

Materials

  • pencil
  • 3 egg cartons (polystyrene, not paper)
  • scissors
  • 3 cups (750 ml) potting soil
  • mustard seeds
  • 1-tablespoon (15-ml) measuring spoon
  • tap water

Procedure

  1. Use the following steps to construct a closable germinating tray:
    • Use the pencil to punch a small drainage hole in the bottom of each compartment of one of the egg cartons.
    • Cut the lid off a second carton. Discard the bottom of the carton. NOTE: Recycle discarded polystyrene.
    • Set the first egg carton in the lid of the second carton so that the lid will catch water draining through the holes.
  2. Construct an open germinating tray from the third egg carton. Repeat the previous procedure, but remove the lid from the egg carton and use that lid to collect drain water.
  3. Fill the compartments of both germinating trays about half full with soil.
  4. Sprinkle a few mustard seeds in each compartment of the trays.
  5. Cover the seeds with about 1 tablespoon (15 ml) of soil.
  6. Moisten the soil in each tray with an equal amount of water. Keep the soil in each tray moist, but not wet, during the entire experiment.
  7. Close the lid of the first germinating tray. Place both trays near a window that receives light most of the day, such as a window facing south.
  8. Observe the open tray daily for the first signs of plant growth.

With and Without

Results

The seeds in both trays germinate.

Why?

During the last stages of seed development, the seed dehydrates (loses water) until it contains very little water. The embryo (partially developed plant inside a seed) ceases to grow and remains inactive until the seed germinates. Thus, germination doesn't mean that a seed comes alive, but rather that the embryo resumes growth and development that stopped during the last stages of seed development.

Mustard is a dicot, meaning it is an angiosperm (flowering plant) and its seeds have two cotyledons (seed leaves). Some dicot seeds, such as mustard, germinate as soon as they are in favorable conditions. Favorable conditions for mustard seeds are sufficient warmth, water, and oxygen. All the seeds in this experiment were exposed to light before being planted. Since the seeds grew in the closed tray, light on the soil was not needed for the seeds to germinate.

Let's Explore

  1.  
    1. Would other dicots give the same results? Repeat the experiment, planting dicot seeds such as radish or beans. Make diagrams of both trays, indicating which type of seed is in each compartment. Science Fair Hint: Continue to make diagrams of the seeds in each tray throughout the experiment to use as part of a project display.
    2. Would not covering the seeds with soil affect the result? Repeat the previous experiment, filling the containers with soil. Press the seeds into the surface of the soil, but do not cover them with soil.
    3. With and Without

      Use a magnifying lens to observe and study the seeds daily.

    4. Would monocot (angiosperm whose seeds have one cotyledon) seeds give the same results? Repeat the previous experiments using corn kernels.

Show Time!

Does the depth that the seeds are planted affect the results? Fill two H)-ounce (300-ml) clear plastic cups with soil. In each cup, plant 4 to 5 pinto beans at different depths so that they are visible through the side of the cup. Place one bean on the surface of the soil. Moisten the soil in each cup with water and keep the soil moist during the experiment. Set the cups near a window. Turn a large Styrofoam cup upside down and use it to cover one of the cups. Observe the seeds daily, quickly lifting and replacing the lid of the covered cup in order to limit the amount of light entering the cup. Display dated photographs and/ or drawings of the seeds to represent the results.

With and Without

Check It Out!

Some seeds will not germinate until they are exposed to light before planting. Plowing a field or cultivating the soil in a garden usually results in plant growth, partly because turning the soil exposes the seeds in the soil to light. Find out more about the effect of light on seed germination. Does the color of light affect germination? For a method of discovering the effect of different colors of light, see page 79 in Janice VanCleave's Plants. (Wiley: New York, 1997).

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