IT is a well-known fact that the nitrogen content of the medium is one of the limiting factors in fungal decomposition. Two experiments were carried out in order to determine whether the effective destruction of wood by Merulius lacrymans is sustained solely by the amount of nitrogen originally present in the wood, or whether any fixation of nitrogen from the atmosphere might possibly occur. Small cubes of wood were used in Exp. 1 and wood shavings in Exp. 2; the procedure, largely the same in both, was as follows: