Stomata are most sensitive to blue light, the light predominating at sunrise. Very low levels of light at dawn can cause stomata to open so they can access carbon dioxide for photosynthesis as soon as the sun hits their leaves. Stomata are closed in the dark in most plants. Light вЂ“ Stomata are triggered to open in the light so that carbon dioxide is available for the light-dependent process of photosynthesis. If this loss of turgor continues throughout the plant, the plant will wilt. This condition causes the leaf to lose turgor or firmness, and the stomata to close. Plants cannot continue to transpire without wilting if the soil is very dry because the water in the xylem that moves out through the leaves is not being replaced by the soil water. Plants with adequate soil moisture will normally transpire at high rates because the soil provides the water to move through the plant. Soil water вЂ“ The source of water for transpiration out of the plant comes from the soil. Therefore, warmer air will increase the driving force for transpiration and cooler air will decrease the driving force for transpiration.

Because cooler air holds less water, its relative humidity increases or it is вЂmoister airвЂ™.

Because warmer air can hold more water, its relative humidity is less than the same air sample at a lower temperature, or it is вЂdrier airвЂ™. The amount of water does not change, just the ability of that air to hold water. As temperature increases, the water holding capacity of that air increases sharply. Temperature вЂ“ Temperature greatly influences the magnitude of the driving force for water movement out of a plant rather than having a direct effect on stomata. When RH is high, the atmosphere contains more moisture, reducing the driving force for transpiration. The lower the RH, the less moist the atmosphere and thus, the greater the driving force for transpiration. Any reduction in water in the atmosphere creates a gradient for water to move from the leaf to the atmosphere. A hydrated leaf would have a RH near 100%, just as the atmosphere on a rainy day would have. Relative humidity вЂ“ Relative humidity (RH) is the amount of water vapor in the air compared to the amount of water vapor that air could hold at a given temperature. Others alter the plantвЂ™s ability to control water loss. In addition, leaves that develop under direct sunlight will have much thicker cuticles than leaves that develop under shade conditions.Д®NVIRONMENTAL CONDITIONS вЂ“В Some environmental conditions create the driving force for movement of water out of the plant. In general, plants from hot, dry climates have thicker cuticles than plants from cool, moist climates. Cuticle thickness varies widely among plant species. The thicker the cuticle layer on a leaf surface, the slower the transpiration rate. Because the cuticle is made of wax, it is very hydrophobic or вЂwater-repellingвЂ™ therefore, water does not move through it very easily. For example, plants from desert climates often have small leaves so that their small boundary layers will help cool the leaf with higher rates of transpiration.Д¬uticle вЂ“ The cuticle is the waxy layer present on all above-ground tissue of a plant and serves as a barrier to water movement out of a leaf. Boundary layers increase as leaf size increases, reducing rates of transpiration as well. Some plants possess stomata that are sunken into the leaf surface, dramatically increasing the boundary layer and slowing transpiration. Leaves that possess many hairs or pubescence will have larger boundary layers the hairs serve as mini-wind breaks by increasing the layer of still air around the leaf surface and slowing transpiration rates. Plants can alter the size of their boundary layers around leaves through a variety of structural features. The larger the boundary layer, the slower the rates of transpiration. For transpiration to occur, water vapor leaving the stomata must diffuse through this motionless layer to reach the atmosphere where the water vapor will be removed by moving air. When stomata are open, transpiration rates increase when they are closed, transpiration rates decrease.Д«oundary layer вЂ“ The boundary layer is a thin layer of still air hugging the surface of the leaf.

Special cells called guard cells control each poreвЂ™s opening or closing. Stomata вЂ“ Stomata are pores in the leaf that allow gas exchange where water vapor leaves the plant and carbon dioxide enters.

Meaning behind leaf on the wind