The total length of all the roots of a large oak tree, for example. will be several hundreds of miles. The functions of the roots are not only to provide anchorage in the ground for the tree, but, more importantly to obtain and provide the minerals and water necessary for its well-being. If normal sources of water adjacent to the tree dry up, the root system will spread in a remarkable effort to discover alternative supplies. As an extreme example, it is on record that tamarisk roots were found 100 feet below ground surface when the Suez Canal was excavated. In more recent studies.
Water is contained in all the tissues, both dead and alive.
But although the formation of 100 grams of cellulose requires 55 grams of water, a tree will lose correspondingly by transpiration almost 100,000 grams of water, or one thousand times as much as its gain in weight. It is this dramatic process of transpiration activated by solar energy, that is responsible for drawing water from the root system to the topmost leaf of the tallest tree, as high as 350 feet above the ground in the case of California redwoods. The process is automatically controlled by nature. For each type of tree a certain amount of water is regularly required for transpiration and, to a minor degree, for tree building. It is this insistent demand that causes the spread of root systems when normal water supply is reduced.