1. Show the students a plant that is beginning to wilt. Ask the class to describe the plant. What does it need? (Water.) What will happen to the plant after water is added? (It will perk up and become firm and upright again.) How did the plant absorb the water? How did it travel to the rest of the plant? (Through the roots and then up through the 'plumbing' or vascular system in the stem.) Explain that one of the main functions of the stem is to transport water and minerals. Tell the class they will set up several experiments that will let them see the plumbing system in several plants.
2. Divide the students into small groups. Give each group several clear plastic cups and red or blue food coloring. Direct them to fill their cups with a few inches of water and add enough food coloring to make a brightly colored solution.
3. Show them a selection of plants you have cut and put in vases of water. Ask them to choose one of each plant stem to place in their cups of colored water. For older students, let them choose and cut a few plant stems on their own.
4. Ask the groups to make predictions on whether or not the colored water will travel up all stems. Will it travel at equal rates in all stems? If not, which will be the fastest? Which will be the slowest? Will the leaves effect the rate of travel in the different plant stems?
5. Have them check their plants at two or three hour intervals. Ask them to hold the plant stem up to a bright light to see whether they can determine and measure the height of the colored water. Record measurements for each plant. Ask the students to guess how long it will take for the color to reach the top of the plant. Leave the plants overnight.
6. To conclude, have the students cut thin cross sections of the various stems and observe the plant pipe patterns with a hand lens or microscope. Have them cut the stem lengthwise to view the plant pipes. Have them make drawings of the cross section and lengthwise section. How did their results compare to their predictions? Can they make any conclusions about the trasport of water through plant stems?
a. Challenge the students to make multi-colored flowers. Provide them with white carnations, food coloring, plastic cups and water. They will need to split the stem at the base into two or more sections and place the different sections into different colored cups of water. Encourage the students experiments with combinations of food coloring to create new colors.
b. Try coloring the plumbing systems in other plant parts. Use roots like carrots, preferably with the leaves still attached, fruits like zucchini, and other unusual stems such as onions.
c. Show the students a log which has been cut in half and has a piece sliced off the rounded edge. Explain to them that the lines and patterns they see in the wood are the plumbing system of the tree. Divide the students into small groups and pass out several pieces of wood and lumber to them. Have the students carefully observethe grain of wood in their piece. If necessary, have them quickly sand and oil the pieces to get a better look. Have them guess where in the tree this piece of wood came from. Have the groups compare their pieces of wood and guesses as to the original orientations.