Five separate X-ray investigations of wood are described. In the first, the SHERRER tube is used, The gitter constants and dimensions o( the unit crystal are calculated. In the second, the causes of the various diffraction patterns of the wood are explained. In the third, the relation between the strength of woods and LAUE or Powder atterns of diffraction figures are discussed. In the fourth, a method of determining the inner strain distribution in wooden material without damaging it, is described. In the fifth, the absorption coefficients of many species of wood are measured and compared with values calculated theoretically.