Use an Erlenmeyer flask. Fill 250 ml with water. Insert 2 or 3 leaves. Cover the top with foil so water will not evaporate from the flask. Place 2 feet from a floodlight. If the plants are too close the leaves could burn. In 24 hours you should see a visible change. Measure the amount of water left in each flask and record the ending volume. I have found that after 3 days the leaves begin to deteriorate. So do not leave this set up over a weekend. 48 hours is the maximum time to let the water transpire. Measure the mass of the leaves after transpiration is finished. You will probably have to fold the leaves to get the long cattails on a scale. Folding them breaks the xylem so they can not transpire water.

Cut 1 inch sections of iris and cattail leaves. Students can observe external texture and internal structures. Have students split open the leaves and draw what they see or tape their sample to the paper. Cattails have internal air passage ways that help roots get oxygen.