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Introduction Leaves are the key for photosynthesis in most plants. Leaf surfaces are equipped with small openings or pores called stomata, which allows carbon dioxide to enter the leaf and oxygen to escape to help photosynthesis. (See Appendix, picture 1) Water is lost through stomata during a process called transpiration. It is estimated that approximately 99% of the water absorbed by the roots of the plant is lost by the leaves in transpiration. To reduce water loss the leaf has a waxy cuticle on the upper epidermis, which is waterproof. (See Appendix, picture 2) The number of stomata on leaf surfaces varies widely among different species of plants. Generally, the lower epidermis of the leaf tends to have a higher total than the upper surface. In this assignment I will try to prove this prediction. In this experiment, leaves from two species of trees will be collected and the number of stomata on the upper and lower epidermis of each leaf will be counted. Stomata opening and closure depends on changes in turgor of the guard cells. If water is drawn into the guard cells by osmosis the