Here are two interesting pictures of bamboo culms. The left culm is the bamboo which rod makers use, the so called Tonkin bamboo. The other (right culm) is a regular bamboo, probably used for making fences and/or as decoration in gardens etc.
As you can see, the Tonkin has a much higher density of the so called power fibers at the outer part near the surface. Tonkin is one of the many spieces of bamboo and only grows in a small area in the Guangdong province of China. It seems that LESS than 1% of the Tonkin harvested is suitable for rod making. Check out this posting for more information on Tonkin.The two most well known companies specialized in importing Tonkin cane for rod building are probably Charles H. Demarest (since the 1930's!) and more recently Andy Royer.
