The factors responsible for the relative resistance of plants to aphid attack are not very well known. Chemical analyses of several varieties of peas indicate that the quantity of nitrogenous constituents in plant juice is proportional to the susceptibility of the plant to aphid attack. These tests hare also demonstrated that amino acids represent the major portion of the soluble nitrogenous constituents in the plants studied.

By the method of paper partition chromatography, several qualitative and semi-quantitative analyses were made of the amino acids in juice extracts of two varieties of peas and of pea aphids feeding on these varieties. This particular method of chromatography, first developed in England in 1944 by Consden, Gordon, and Martin (1), and modified since by other workers (2, 3), was found very effecrive for these studies.