This lesson is designed to lead students to understand what the forest means to humankind. It is important that they see the forest not only for its products, but also for the environmental benefits and intangible rewards it provides. The day before beginning this lesson, ask the students to list everything they touch while at home that evening that is in some way derived from trees. You may wish to reinforce this project with Project Learning Tree Activity 37 in the manual for Grades Pre K-8.
Trees take up large quantities of water from the soil.
Some is used in the photosynthetic process, some is used as a solvent to transport minerals and nutrients, but most is incorporated in the protoplasm of the tree cells. This occurs mostly from the leaves, and the transpiration rate is highest during hot afternoons in the growing season. The transpired water is constantly being replaced by water brought from the soil. When transpiration occurs more rapidly than water replacement, the tree will wilt. Tie a plastic bag around the end of a leafy twig and leave it for 24 hours.