Transpiration

Plants are found in almost every ecosystem in the world from deserts, to temperate forests, and down to the bottom of the sea. As a consequence of natural selection plants have evolved a stunning diversity of adaptations to deal with different environmental challenges. One of the key challenges plants face is maintaining proper hydration. Water is a critical resource that they depend upon for photosynthesis, structural support, and the transportation of nutrients and other important molecules. One way that plants can control their water balance is by regulating a process known as transpiration, which is essentially the evaporation of water from the aerial parts of a plant. This loss of water occurs primarily from pores on the leaves called stomata. But how does the water get here?

To answer this question let's look more closely underground. Here water enters the plants roots by osmosis then moves all the way up to the leaves through a vascular tissue called xylem. This channel of water is known as the transpiration stream. Because water molecules stick to each other and to the xylem walls, when it evaporates from stomata water from lower in the transpiration stream is pulled upward