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This week let's continue tree science (see previous tree science post) by investigating water movement through trees, and learning how to measure the height of a tree.

1. Tree Transpiration

Transpiration is a fancy word for the movement of water out of trees and other plants. Did you know that almost twice as much water enters the atmosphere through plants as through the surface of the oceans? (Another benefit of trees!)


  • a nearby tree (outside) with branches you can reach
  • clear plastic baggy for each child
  • chenille or twist tie to hold bag around branch (enough for each child)

You might want to gather enough of these materials to compare branches on different parts of the tree and/or branches on different types of trees. (You will see the best results on a hot, sunny day.)

Place the bag over the tip of a branch so that it contains at least one leaf. Use the chenille or twist tie to close the bag around the branch to hold it closed. Make a prediction about what will happen. Now wait for 15 or 20 minutes and check the bag. See anything? Try again after 1/2 hour.

The bag should fill with moisture and condensation. Each tree leaf has tiny holes called stomata. Moisture exits the holes not only to cool the tree (like our sweat does for us), but also to help plants move materials up from the roots.

Were there any differences between different parts of the tree or different kinds of trees? What do you think would happen if you did the same experiment at night?

You can also perform this experiment indoors if you place a cut tree branch in a water-filled vase. Be sure to place the tree branch in a sunny window or under a bright lamp to encourage water movement into the plastic bag.

Extension (for older students):

Make up and perform experiments to test the factors that influence transpiration:

  • temperature
  • sunlight intensity
  • water supply
  • tree growth rate


Where does the water come from?

Most plants and animals need a lot of water every day. Trees absorb the water they need through their roots and then move it up to the leaves through the xylem.

2. Measure the height of trees

How far does the water have to travel from roots to top of the tree?

There are several different methods to measure the height of any tall object, including a tree.

Method 1 (requires math):


  • a stick
  • a tree that is apart from other trees (so you can see its entire shadow at least one time of day)
  • tape measure (longer the better)
  • paper and pencil

For this activity, you will need a sunny day. Place the stick upright in the ground near the tree. Use the tape measure to measure the height of the stick from the ground, and the length of the resulting shadow from the base of stick. Also measure the longest length of the tree's shadow from the base of the tree. Assuming the two ratios are the same, solve for the height of the tree by multiplying the length of the tree's shadow x (the height of the stick/the length of the stick's shadow). See the illustration:



I found this video that discusses another method. You will need a second person to help you and a measuring tape.

Now, how far does the water need to move? If you take into consideration that a tree's root may be a large or larger than its crown, then a tree one hundred feet tall may have to move water two hundred feet or more. That one big straw!

Let me know if you have any questions or other methods for measuring trees.

Don’t you love going to the grocery store this time of year, with all the pretty pumpkins and fresh apples? Wouldn’t it be fun to use some pumpkins and apples for science activities?


  • Pumpkins and apples. Get some different sizes, kinds and colors, if possible.
  • Bathroom/kitchen scale (depending on activities you choose)
  • Container, such as a large plastic bin, to hold water
  • Age-appropriate cutting implement
  • Trays for holding fruit parts
  • Paper
  • Pencils/crayons.

Activity 1. Exploration/Botany Vocabulary
Have your children look at the pumpkins and apples. How are they different, how are they the same?

Both pumpkins and apples are fruit. They both have seeds inside. Both have stems, can you find the stem? What is the stem for? Apples have a skin, does a pumpkin? (Yes, it does). You can ask older children what they think the fleshy meat (the part we eat) is for. Do both pumpkins and apples have a flower or blossom end?

Activity 2. Sorting
Have the children sort the pumpkins from the apples. They can also sort the sizes, from smallest to biggest, or by color. (Sorting is such an important scientific skill, one that tends to get forgotten.)

Activity 3. Weight Estimation
Have the children estimate how much they think each pumpkin/apple weighs. Ask them how they would weigh a big pumpkin.

Help them weigh the pumpkins and apples.

Activity 4. Pumpkin/Apple Floating
Will a pumpkin float? Will an apple float? Does how big it is determine whether it floats or not?

Fill up a large container with enough water to float the biggest pumpkin without slopping over. See if the different fruit will float or not. Have the children bob for apples, if appropriate. Have the children draw what happened.

Activity 5. Seed Estimation
Have the children estimate how many seeds they think are inside each pumpkin or apple before you cut the fruit open. Write down the estimations and compare with the results when you open them in the next activity.

Activity 6. Pumpkin/Apple Exploration
Begin to cut into the pumpkins by cutting around the stem, like you were going to make a jack-o’-lantern. Allow the children who want to explore to get their hands inside. Let them feel the seeds.

Cut the apples and allow the children to search for seeds. Have them count the apple seeds. See if slices will float differently than whole fruit.

Activity 7. Let It Rot!
Rotting or decay is a mysterious and fascinating process for children. In our modern ultra-clean world of antibiotics and hand sanitizers, we forget what an important process it is. If at all possible, find a quiet corner in the yard and let the pumpkin or apple rot. Check the progress daily. Admire the molds that develop. Discuss the odors. If rotting isn’t progressing, add a bit of water.

Activity 8. Grow or Eat the Pumpkins Seeds
You might want to save some of the pumpkin seeds to grow. If so, wash them and let them dry. Don’t heat them/cook them if you want to plant the seeds. Check one of the websites below for more information on growing pumpkin seeds.

Activity 9. Eating

You can oven-dry some of the pumpkin seeds for eating.

Celebrate Fall by making some of your favorite recipes. Here’s one of ours:

Pumpkin Pie in a Glass Smoothie

Add to blender:

1 to 1 1/2 cups canned or pureed cooked pumpkin
2 cups milk, soymilk or ricemilk
1/3 cup sweetener such as maple syrup
1 cup tofu
1 tsp cinnamon
dash nutmeg
1/4 tsp cloves

Blend until well mixed. Makes 4 8oz. Servings.

Early Learning Ideas website has many more excellent lessons for preschoolers.

Related Books:

Pumpkin Circle: The Story of a Garden by George Levenson, Shmuel Thaler (Photographer)

I love this book because it isn’t afraid to show rot.

Check this list of Fall–inspired books from the MissRumphiusEffect Blog.

Patty's Pumpkin Patch by Teri Sloat

Follow the progress of a pumpkin patch through the seasons while finding items from the alphabet. For example, in the field where the pumpkins are being planted, “a” is for ant and “b” is for beetle.