Basketry is probably the oldest and most wide-spread craft and art developed by the Native Americans. Baskets can be made from many kinds of materials, but generally plant stems, either whole or split, are used. In some cases the stems or stalks are peeled for the bark or interior fibers, or root fibers and leaves and grass stems are used. Baskets can be woven out of almost anything, but it requires great skill and much knowledge. The roots, stems, bark, leaves and flowers of different plants produce the broad range of colors in most baskets. Identical plant materials gathered in different seasons may produce different colors. Some basketmakers used commercial dyes to obtain colors not available from plants or to alter or intensify the effects produced by vegetal material. But most basketmakers today prefer to produce their colors in traditional ways or experiment with plants near their homes. Basketmakers must be knowledgeable about which plants in their area are suitable for the kind of baskets the maker intends to create and the colors desired: where they grow, their special properties, the best season to gather them, and how they must be processed and stored. This kind of knowledge is passed down from one generation to the next.