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Allelopathic activity of aromatic plants has been described frequently.Essential oils inhibit germination and growth of various plants.Residues of leaves of aromatic plants in soil inhibit the growth and the emergence of seedlings.We have developed a good quantitative assay to test for the inhibitory activity of volatiles on seed germination and have screened dozens of essential oils and their components.The major active allelochemicals were found to be aldehydic and ketonic monoterpenes,having a α-β unsaturated double bond,such as citral,(geranial and neral) and pulegone.Exposure of seeds for 4h to the compounds was enough to cause inhibition of the rate of germination and of seedling development in wheat,Amaranthus palmeri and Brassica nigra.Using histochemistry,we observed that citral is absorbed by wheat seed through the abscission layer,and that it reaches highest concentration in the embryo,where it accumulated in the aleurone,scutellum and parts of the endosperm.After exposure of wheat seeds to pure components of essential oils,GC-MS analysis of extracts of the seeds showed the presence of new products in the endosperm and embryo.These were probably formed by the metabolic detoxification of the inhibitors by the seed.The derivatives of the toxic compounds usually found in the seeds were less toxic than the original compound.Detoxification occurs in both embryo and endosperm during the first day of imbibition.In field studies,in which known amounts of residues of aromatic plants were mixed with soil in which wheat seeds sown,some components of the essential oil and their derivatives were found in the seed embryo and endosperm.The agrotechnology aspects will be discussed and further work of formulation and application of essential oils as bio-herbicides will be present.