Early humans with few or no tools could have used many of these plants. Young branches of willows are so flexible and strong they can be used to tie bundles of firewood together. Even young children learn to weave strips of plant material into flat mats; with some skill they can weave material into baskets, bowls, and ropes (FIGURE 24-39). With such simple techniques, fibrous plant parts can be used to make shelters, baskets for carrying or storing food, even rough clothing. If baskets are woven tightly and rubbed with pine resin or clay, they can be made sufficiently waterproof to store water. It did not take humans long to learn how to strip the useful fibers out of plants and convert them into finer material for careful weaving and construction. Even today we still rely on plant fibers in our daily lives.