One popular method of showing that a plant will lose water through its leaves is to secure a plastic bag around four or five leaves with tape. Place the plant in the sun for a few hours each day; you can also use a sunlamp. Water will begin collecting in the bag, and the bag may become cloudy. Measure the amount of water in the bag each day and take a picture of it.
One of the effects of transpiration is humidity. Some trees can lose thousands of pounds of water in a single day, and the water has to go somewhere. Humidity is measured with a hygrometer, a small, inexpensive device. Gather several house plants and put them in a lighted area close together. After a couple of hours, read the humidity in that area with a hygrometer and compare it to another part of the room where there are no houseplants.
An experiment to demonstrate the cause of transpiration can be done using clippings from a bush or tree. Make two leafy clippings that are about the same size and place each in its own tightly sealed plastic bag. Place one in a window and the other in a cupboard and check them from time to time. Which will collect more water? The same can be done outdoors with one bag wrapped around a leafy stem in a sunny place in the yard and the other in a shady place.
Use food coloring and water to turn a white flower blue, purple, green or any other color. Fill a glass with water and use water-soluble food dye to color the water. If you like, fill several glasses with different colored water. Place the stem of a white flower in the water and allow it to sit for about six hours. The colored water will travel through the stem and into the flower, turning the petals a new color. Experiment further by placing one of the flowers in the refrigerator to find out if it slows down the transpiration process.