to its leaves, according to the cohesion-tension theory. The upward movement of water and solutes (hydraulic lift) is regulated in the roots by the endodermis and in the plant foliage by stomatal conductance, and can be interrupted in root and shoot xylem vessels by cavitation, also called xylem embolism. In addition, the high concentration of salts within plant roots creates an osmotic pressure gradient that pushes soil water into the roots. Osmotic absorption becomes more important during times of low water transpiration caused by lower temperatures (for example at night) or high humidity, and the reverse occurs under high temperature or low humidity. It is these processes that cause guttation and wilting, respectively. Root extension is vital for plant survival. A study of a single winter rye plant grown for four months in one cubic foot (0.0283 cubic meters) of loam soil showed that the plant developed 13,800,000 roots, a total of 620 km in length with 237 square meters in surface area; and 14 billion root hairs of 10,620 km total length and 400 square meters total area; for a total surface area of 638 square meters. The total surface area of the loam soil was estimated to be 52,000 square meters. In other words, the roots were in contact with only 1.2% of the soil volume. However, root extension should be viewed as a dynamic process, allowing new roots to explore a new volume of soil each day, increasing dramatically the total volume of soil explored over a given growth period, and thus the volume of water taken up by the root system over this period. Root architecture, i.e. the spatial configuration of the root system, plays a prominent role in the adaptation of plants to soil water and nutrient availability, and thus in plant productivity. Roots must seek out water as the unsaturated flow of water in soil can move only at a rate of up to 2.5 cm per day; as a result they are constantly dying and growing as they seek out high concentrations of soil moisture. Insufficient soil moisture, to the point of causing wilting, will cause permanent damage and crop yields will suffer. When grain sorghum was exposed to soil suction as low as 1300 kPa during the seed head emergence through bloom and seed set stages of growth, its production was reduced by 34%. Consumptive use and water use efficiency Only a