... are at the time. Externally many things effect transpiration, such as; 1. Temperature High temperatures encourages evaporation of water from the mesophyll cells 2. Relative Humidity, the degree to which the atmosphere is saturated with water vapour. This is important because it determines the saturation deficit, the humidity difference between the inside and outside of the leaf. As evaporation precedes from the mesophyll cells the air within the sub-stomatal air chambers develops greater saturation. There will be a concentration gradient dependent on the humidity of the surrounding atmosphere. This will dictate the rate water transpires out through the stomata. Plant species have adapted to suit their environment via natural selection. Plants in dry/arid habitats such as Cacti have cut down the number of stomata, and lowering their evaporating surface areas. In the other direction plants in a rain forest have developed far larger surface areas and greater number of stomata to allow ...

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