The principal parts of the grain of two varieties of wheat and two varieties of maize have been separated by manual dissection and the nicotinic acid of the fractions assayed microbiologically. It is shown that the aleurone layer contains 82% of the total nicotinic acid in wheat and approximately 60% in maize. The scutellum contains 1.3% of the total in wheat and, because of its greater bulk, approximately 11% in maize. The carbohydrate endosperm of sweet maize showed a concentration of nicotinic acid twice that of flint maize, though the total nicotinic acid content of each type was similar. Dissected embryos of wheat have grown to flowering successfully, though weakly, without any external supply of nicotinic acid, though 99% of the nicotinic acid of the grain is thereby dispensed with. The provision of an external supply had only a slight stimulating effect.