The rate of transpiration is measured as the amount of water lost/ square meter/ minute. Because water evaporates through the many stomata on the leaf surface, the rate of transpiration is directly related to the surface area. To arrive at the rate of transpiration, therefore, you must calculate the leaf surface area of each plant: Because most stomata are found in the lower epidermis, you will determine that surface area.
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Lay the leaves to be measured on a 1cm grid and trace their outlines. 
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Count the number of square centimeters. Estimate the area of the partial squares. (Here's a simple method for this estimate: Count a partial square if it is at least half covered by the leaf; do not count partial squares that are less than half covered.) 
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Do not include the area of the stem (petiole) in your calculations. 
What is the surface area of this leaf in cm^{2}?
