1. The genus Vicia may be subdivided into groups of species characterized by associations of ninhydrin-positive compounds occurring in high concentrations in their seeds. Despite these subdivisions the overall distribution pattern emphasizes the unity of the genus and the possible value of such studies in establishing degrees of relationship between species within the genus. 2. Canavanine is a major constituent in the seeds of 17 species. 3. gamma-Hydroxyarginine, an amino acid that has not been found in other plant genera, occurs in 18 species. 4. gamma-Hydroxyornithine, a new natural amino acid, is found in two species. 5. A new naturally occurring ureido amino acid tentatively identified as; gamma-hydroxycitrulline' is found in two species. 6. High concentrations of alphabeta-diaminopropionic acid are found in seed of V. baicalensis and of alphagamma-diaminobutyric acid in seed of V. aurantica. 7. The neurotoxic amino acid beta-cyanoalanine and its gamma-glutamyl peptide are found together in high concentrations in the seeds of 16 species of this agriculturally important genus. 8. Seven unidentified ninhydrin-positive compounds occur in high concentration (about 1% of the dry weight or more) in the seed of various species. Details of their R(F) values, ionic mobilities and colour reactions are given. 9. The total concentration of extractable ninhydrin-positive compounds varies little between seeds of different species and these compounds may, as has been suggested for those in Lathyrus, constitute a readily available form of storage nitrogen. 10. The nature and distribution, as opposed to the total concentration, of the amino acids and related compounds accumulated in the seeds of Vicia are different from those accumulated in the seeds of the related genus, Lathyrus. One particularly interesting difference is the accumulation of C(6) guanidino amino acids (arginine and gamma-hydroxyarginine) by Vicia and the accumulation of C(7) guanidino amino acids (homoarginine, gamma-hydroxyhomoarginine and the related amino acid lathyrine) by Lathyrus. Such differences afford a method for distinguishing between species of these genera.

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