SUMMARYThe beneficial effect on the growth ofMorchella crassipesof the addition of natural materials to a medium of mineral salts, dextrose, vitamins of the B complex, and purine and pyrimidine bases is because of the ash of the natural products. Manganese and calcium are primarily concerned. The complex interrelations between pH, Mn, Ca and chelating agents on the growth ofM. crassipesare discussed. The ash of natural products is identified as the“filtrate factor”for this fungus.