Transpiration

Transpiration is the process by which plants transport water from the soil through the roots, up the stem, and out the leaves. This is important to plants because water is a crucial ingredient for photosynthesis, as well as a solvent for the products of photosynthesis. Because plants are unable to move to areas with more water, they are dependent upon their root systems to find water underground. Because of this situation, the root systems of some plants can extend over a hundred feet below ground.

Cacti and other plants that live in arid environments are in a special situation. Though water is just as essential to them as it is to other species of plants, they live in areas where water is scarce. Their only means of obtaining water is through transpiration. However, this means that some of the water will quickly be lost to the dry air. Cacti overcome this problem by greatly reducing their leaves (the spines of a cactus are the leaves), using a variation of photosynthesis called Crassulacean acid metabolism, possessing succulent tissues that hold a large amount of water, and opening their stomata only at night. Using these methods, cacti are able to perform the transpiration necessary, even in the driest conditions, without dessicating.