Transpiration in botany refers to the evaporation of water from the leaves of plants, primarily through their adjustable stomata (hence 'stomatal transpiration'), but also through their outer surface (cuticle, hence 'cuticular transpiration'). The amount of water transpired over a specific period is known as the transpiration rate. In plants, water is generally released through specialized adjustable openings, the stomata, with the extent of water loss varying by more than two orders of magnitude among different plant species and depending on the specific location of the plants. The so-called stomata consist of two guard cells that contain chloroplasts. The regulation of the stomata is controlled by turgor (cell pressure). This regulation is particularly important, as otherwise, the plant would lose too much water and thus dry out. In warm regions, there are special adaptations for plant transpiration, as plants constantly face the challenge of needing to take in CO2 through the stomata while also losing water. To mitigate this issue, many plants have sunken stomata with specialized hairs. Illustrated with 28 black-and-white images. Reprint of the original edition from 1904.