Do trees release sweat

People sweat to cool down when our body temperature rises. Do trees release sweat when they're hot, too?

What You Need: One resealable, clear, plastic bag A leafy tree branch that is easily accessible A hot and sunny summer day

What You Do: This activity is very simple but can be so much fun. Demonstrate how people cool down when their body temperature increases. You can play a brisk game of tag and have them feel their foreheads after running around. Are they hot and sweaty? Explore the same idea using a tree. On a hot and sunny day, place the plastic bag over the leaves of a tree. The bag should cover above and below the leaves. Leave the bag in place until you see little beads of moisture collect on the side of the bag. This may take a couple of hours.

What Happened: Trees drink water from the ground, as much as 100 gallons per day. When the temperature increases, the tree releases moisture. Leaves of trees have pores, much like the skin on people. The pores on the leaves react to the temperature in their environment. If the air temperature decreases, the pores will contract, or close. In a warm environment, like the one you created with the plastic bag, the pores will expand. The pores release moisture when they expand, a process called transpiration. In our experiment, the moisture collects on the side of the bag, making it easy for us to observe the process.

A Step Further: Consider other ways in which trees are like or unlike people. People take in oxygen and breathe out carbon dioxide. Trees take in carbon dioxide and release oxygen.

If you use an upside down glass placed against the tree trunk, you may be able to hear the sap in the tree moving. It reminds us of hearing our own heartbeat with a stethoscope.