But no tree has held so dear a place in the hearts of the people, or been so watchfully cared for as the old "Washington Elm" still standing in Cambridge, Massachusetts. Under it Washington took command of the continental army. It is visited every year by hundreds of persons, who stand with uncovered heads beneath its spreading branches. Many years ago it was struck by lightning and the upper part torn off, but all the broken edges have been sealed with pitch to stop decay. It has been covered with fine wire netting to prevent the bark being chipped off by relic hunters. It is carefully guarded from damage by insects, and the boughs are stayed by strong wires. And so we might name many instances of trees that are loved and cared for on account of their beauty, stateliness or some event connected with them, but it is the usefulness of trees that we shall mention in this chapter. In the larger use of forests is included their effect on climate and rainfall. It is generally believed that clouds, passing over the damp, cool air that rises from a forest, are more likely to be condensed into rain, and so we can establish the general rule that the country which is well wooded will probably have a larger rainfall than the one which has few trees. Twenty-five years ago Kansas was a prairie state with few trees, and the semi-arid plains extended half-way across the state, but thousands of acres of trees have been planted, and crops have been cultivated, and the more forests and crops the farmer plants the more rain comes to water them. The great droughts which used to ruin their crops year after year no longer disturb them. The hot winds which could undo a whole season's hard work in a day are seldom heard of now. Kansas is no longer in the semi-arid region. It is one of the most productive states in the Union, and this has come, not by dry-farming, but by the cultivation of the soil and by the planting of trees. Though rainfall increases, destructive floods become fewer, for the humus and the leaves on the ground in the forests hold the water as in a vast sponge, and, as we have seen in the preceding chapter, they keep the waters in check and distribute the rainfall gently and evenly on the lands below. They thus prevent erosion of the hillsides and balance the water supply of rivers. Trees supply us with food and medicine, and greatest of all their direct uses, they furnish lumber for all kinds of manufacturing.