The stems of the three different plants (mesophyte, hydrophyte and xerophyte) have all adapted in different ways in enable the plant to flourish in its given environment. The stem of an oak tree is strong in order to hold up the plant and the vascular bundles are well developed. The stem of a Water Lilly is very different to the stem of an oak tree as it lives in an environment full of water. The stem of the water Lilly is weak and hollow allowing the plant to float in the water, and its vascular bundles are undeveloped(1). These contrasts to the stem of barrel cactus that is succulent and round shaped that has many dips and groves in it, its vascular bundles are also well developed like the oak tree. The stem of an oak tree is strong and thick so that it can hold up all the branches at the top of the tree so the leaves are all exposed to sunlight allowing the plant to have enough energy to carry out photosynthesis. The vascular bundles contain xylem and phloem the phloem is used to transport minerals around the plant and the xylem is used to transport water. The xylem is important as it transports the water from the roots of the plant up to the leaves and stem where it’s used in photosynthesis and in cell division that allows the plant to grow. The water is able to move up the plant against gravity due to the transpiration pull as when water is evaporated from the leaves more water is pulled up from the roots due to the cohesion acting on the water molecules. This is a contrast to the stem of the Water Lilly where the vascular bundles of the plant are undeveloped as the plant does not need to move water from the roots to the leaves instead water can just move straight into the leaves and top of plant via osmosis as the plant is surrounded by water, it would be a waste of energy if the plant had developed xylem vessels as transport of water is not necessary(2). The stem is also weak and contains little lignin tissues as the water supports the plant as if the stem was rigid and not flexible then the plant would break in changing currents, the stem of the Water Lilly is also hollow to allow storage of gases that give the plant buoyancy. The stem of a barrel cactus is different to both of these stems as it is a round shape that looks a bit like a barrel, hence its name. The stem also has multiple pits and groves that contain the stomata, and also help shade the plant from the intense heat. The stem is succulent and is able to store large amounts of water, the vascular bundles are well developed as like the oak tree water must be transported from the roots around the plant where it is used in processes like photosynthesis(3).The stem of the barrel cactus also has a thick waxy cuticle that prevents water loss by slowing down the rate of evaporation as the waxy cuticle acts as a protective layer trapping water inside the plant. (4) All three of these plants stems have adapted in different ways to keep water balance within the plant the oak tree has strong stems and developed xylem vessels to transport water around the plant and keep water balance. The stem of a Water Lilly is hollow and weak with little lignin tissues to allow the plant to move in the water, the xylem vessels are undeveloped, as the plant does not need to transport water around the plant in order to keep water balance. The barrel cactus is different to this in the fact that its stem is structured in away to provide shade and humidity around the stomata by having many groves around the plant in order to slow down water loss. The xylem is well developed in order to transport water around the plant to be used in cellular process like photosynthesis and cell division but also to cool the plant down and help it control its water balance, as unlike the Water Lilly where water loss is not a problem water loss must be controlled in barrel cactus in order for water balance to be maintained. All of these plants need water in order to carry out processes such as photosynthesis as water is a raw material in this process. 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. This is why it is so important for water balance to be controlled in the plant, as all these plants will fail to survive if water balance in the plant was not controlled.
(1)http://www.ehow.com/info_8749756_water-lily-adaptations.html
(2)http://loretocollegebiology.weebly.com/mesophytes-xerophytes-and-hydrophytes.html
(3) http://www.conservancy.co.uk/learn/downloads/fieldtrips/xerophytes.pdf
(4)http://www.ehow.com/info_11384273_adaptations-barrel-cactus.html
(1)http://www.ehow.com/info_8749756_water-lily-adaptations.html
(2)http://loretocollegebiology.weebly.com/mesophytes-xerophytes-and-hydrophytes.html
(3) http://www.conservancy.co.uk/learn/downloads/fieldtrips/xerophytes.pdf
(4)http://www.ehow.com/info_11384273_adaptations-barrel-cactus.html