and 10th centuries AD. The history of the tube zithers is interconnected with that of bar-zithers. It may not always be possible to tell from the artwork if a stick or a thin bamboo tube is being depicted on a relief artwork. Basic divisions Tube zithers can be divided by the materials used to create the tube and strings. They can be divided by the method used to get sound from the strings. They can be divided by the way the strings are arranged on the tube, which can interact with the way the strings are sounded. They can be divided by whether the tube is a whole tube or a half tube. Most tube zithers are made from bamboo, a material that is naturally hollow. Other plants have been adapted to make tubes, including cactus and breadfruit trees. Half zithers are made of both bamboo and of curved-wood boards, as much a board zither as a tube zither. After addressing the device used to stretch the strings, a tube as opposed to a stick for a bar-zither, Hornbostel-Sachs divides the tube zithers into two types, based on the types of strings they use: idiochord and heterochord. Idiochord tube zithers have "strings" which are made from the material of the tube itself. With bamboo, the surface of the tube is cut and peeled into strips, leaving both ends still attached to the tube. Small pieces of bamboo are put under the strip to make it tight. The tight strip of bamboo acts as a string and can be plucked, hammered or bowed. Heterochord tube zithers use a separate material for strings, such as wire, fishing line or guitar strings. The strings are secured to the tube on each end, and tension is placed on them. Some resemble the idiochord zithers, the string put through holes in the tube, secured there and bamboo put underneath to make them taut. Another version secures one end through a hole in the tube, the other end wrapped around a peg that can be tightened. Another way of looking at the instruments is the way strings are arranged on the tube. Polychordal tube zithers circle the tube with string-rows. In contrast, parallel-string zithers have strings arranged in parallel, often only one pair for the tube and linked together so that they sound together. Tube zithers may be plucked chordophones, tapped or struck percussion chordophones or