Straight pipes are easier to make than elbow pipes, but have certain disadvantages. They have to be directed upward in smoking to keep the tobacco from falling out of the bowl, and the tobacco dust and juices are drawn down into the stem with results familiar to all smokers. To prevent this, many tribes are said to have put a pebble or pellet of clay in the bottom of the bowl before filling it. Even a slight angle between the bowl and stem is a great convenience to the smoker, and this improvement once hit upon, perhaps through faulty workmanship, the development of the elbow pipe was easy. Pipes from different parts of North America show all degrees of bowl inclination from the straight tube to a right angle, and there can be little doubt that the main evolution of the elbow pipe was along this line. In the Mississippi Valley and Great Plains there are, however, certain types of elbow pipe which could hardly have been developed in this way. In these the bowl rests upon a base which extends out for some distance in front of it. From various archæological finds it seems probable that these types were developed from pipes which had a corn-cob bowl pierced through the base with a reed stem. North American elbow pipes have never been satisfactorily classified, but about twenty types are distinguishable. Only the more important of these can be mentioned here. Most of the types show a more or less continuous geographical distribution, but there was no tribe or region in which all the pipes were of the same type. The Chippewa distinguished four types of pipe which were in simultaneous use among them. These were—(1) Women’s pipes, which were small, with short stems and little decoration. (2) Men’s pipes for ordinary smoking, which were somewhat larger and better made than the women’s pipes, but were also small. (3) Personal pipes of famous warriors, which were larger than the ordinary pipes, with heavy decorated stems sometimes as much as five feet long. (4) Chief’s pipes and ceremonial pipes, which were large, with long stems like the warrior’s pipes, and were elaborately decorated. Even the pipes for ordinary smoking were highly valued and would often be carved and decorated in the owner’s spare time. Stone for pipe-making, and even finished pipes, seem to have been bartered from tribe to tribe in ancient times.