The stomata of the three different plants (mesophyte, hydrophyte and xerophyte) have all adapted in different ways to enable the plant to flourish in its given environment. For example in an oak tree which is a mesophyte plant the stomata stay open most of the time except in extreme conditions where water loss is occurring at a faster rate, such as heat and wind in these conditions the stomata will close, the stomata are located on the bottom of the leaf (1). In a water Lilly (Nymphaeaceae) which is a hydrophyte the stomata will stay open constantly, and are found on top of the leaf (2). Compared to a Barrel cactus, which is a xerophyte where the stomata are almost always closed throughout the whole day and only open at night, the stomata on these plants are found to the stem. These plants stomata are all open at different times and located in different places due to their varying environments. The oak tree grows in an environment where water is not often limited so does not need to control water loss all the time, but only when water is low in which case it can close its stomata due to flaccid guard cells. The stomata are located on the bottom of the stem in order to slow down the rate of transpiration as water evaporates upward so having the stomata located on the bottom of the leaf means water will evaporate slower. The water Lilly grows in an environment where there is an abundance of water meaning the stomata are always open as water loss is not an issue in-fact the plant wants to get rid of water to prevent it from drowning. The stomata are also found on the top of the leaf as the underside is often summered in water. This contracts to the barrel cactus, which grows in an environment where water loss is problem as water is scarce. In these plants the stomata are located on the stem as the plant does not have leaves the stomata are also located in pits, and groves of the barrel shape to try and prevent water loss as in these pits there will be higher humidity so less transpiration will occur (3). The stomata are often open only at night as this is when temperature is coolest so less water will be lost the barrel cactus is a C4 plant meaning it carries out photosynthesis in two different stages which is why it is able to open its stomata only at night, this contrasts to the water Lilly where the stomata are constantly open as water loss is not a problem unlike the barrel caucus where if the plant does not conserve water it will die. All three plants stomata have adapted in different ways due to their varying environments to keep water balance with in the plant. The Water Lilly keeps its stomata open all the time as it lives in abundance of water compared to the barrel cactus which is a C4 who only opens its stomata at night and they are located in the pits and groves of the plant to lessen transpiration and water loss as water is scarce, so if the plant opened its stomata during the day water loss would occur at a faster rate as the heat would cause more water to be evaporated. The oak tree is somewhere in between the Water Lilly and barrel cactus in that it only closes its stomata when its experiencing dry or extremely windy conditions when water loss is a problem but otherwise its stomata are constantly open. All these plants need water in order to carry out life processes such as photosynthesis where water and carbon dioxide are converted into glucose and oxygen using energy from the sunlight. They also need water in order for their cells to stay turgid as plants do not have skeletons like animals do so they relay on their vacuoles being fill of water to keep the upright structure of the plant, this is important as the plant needs to stay upright in order for them to absorb sunlight.
(1)http://plantwaterbalance.blogspot.co.nz/2013/06/mesophytes-adaptations.html
(2)http://loretocollegebiology.weebly.com/mesophytes-xerophytes-and-hydrophytes.html
(3) http://www.ehow.com/info_11384273_adaptations-barrel-cactus.html