The Native Americans of northern California were highly skilled at basketry, using the reeds, grasses, bards, and roots they found around them to fashion articles of all sorts and sizes - not only trays, containers, and cooking pots, but hats, boats, fish traps, baby carriers, and ceremonial objects.
Of all these experts, none excelled the Pomo - a group who lived on or near the coast during the 1800's, and whose descendants continue to live in parts of the same region to the same region to this day. They made baskets three feet in diameter and others no bigger than a thimble. The Pomo people were masters of decoration. Some of their baskets were completely covered with shell pendants; others with feathers that made the baskets' surfaces as soft as the breasts of birds. Moreover, the Pomo people made use of more weaving techniques than did their neighbors. Most groups made all their basketwork by twining - the twisting of a flexible horizontal material, called a weft, around stiffer vertical strands of material, the warp. Others depended primarily on coiling - a process in which a continuous coil of stiff material is held in the desired shape with tight wrapping of flexible strands. Only the Pomo people used both processes with equal case and frequency. In addition, they made use of four distinct variations on the basic twining process, often employing more than one of them in a single article.
Although a wide variety of materials was available, the Pomo people used only a few. The warp was always made of willow, and the most commonly used welt was sedge root, a woody fiber that could easily be separated into strands no thicker than a thread. For color, the Pomo people used the bark of redbud for their twined work and dyed bullrush root for black in coiled work. Though other materials were sometimes used, these four were the staples in their finest basketry.
If the basketry materials used by the Pomo people were limited, the designs were amazingly varied. Every Pomo basketmaker knew how to produce from fifteen to twenty distict patterns that could be combined in a number of different ways.
【題組】7. According to the passage, what did the Pomo people use as the warp in their baskets?