water exaporates frm the leaves and other parts of the plant above the ground. The evaporation of water from the plant is called ''transpiration''. It occurs mainl through the stomata. However, as quickly as water is lost from the leaves, more water enters the roots and flows up the stem. The water flows up the plant in narrow pipes, rather like capillary tubes. These tubes make up the xylem. The walls of the tubes are made of lignin, which is hard and waterproof. In trees and shurbs the xylem tubes are one of the main components of wood. They do not contain living material and are therefore dead.` Water rises up the stem mainly by being ''pulled'' from above. The ''pull'' is created by the evaporation if water from the leaves. If you stop this by, for example, cutting iff the leaves or blocking the stomata, the flow of water up the stem slows down or stops. The drier the atmosphere, the greater is the rate of transpiration. In very dry wather, water may evaporate from the leaves faster than it is replaced from the soil. The plant then suffers from water shortage. Normally a plant's cells are full of water, and all the cells are pressing against each other within the epidermial covering. This helps to support the plant amd holds the leaves out flat. If a plant runs short of water, the cells lose water and go flabby. The plant then droops. This is called wilting. Plants living in dry places have all sorts of adaptations for not
