Characteristic x‐ray diffraction patterns produced by transverse, radial and tangential sections of wood fibers have been discussed. There are two fundamental types of orientation of the micelles or fibrils in wood fibers: A, parallel to the fiber axis; B, parallel to each other, but on a spiral at a definite slope to the fiber axis. The deviation from either type may be qualitatively estimated from the diffraction pattern. For type B, the slope of the spiral may be measured with considerable accuracy. When large angles of slope of the micelles are indicated most wood fibers differ fundamentally from cotton. In wood fibers the average slope is at a definite angle to the fiber axis; the deviation is from Type B. In cotton fibers the average slope approaches 0°; the deviation is from Type A.