When allelochemicals that are released from a plant affect growth or germination of individuals of the same species, the term allelopathy is often replaced by the term autotoxicity. Research on allelopathy started mainly in the 1940s and was eventually continued in the sixties by Muller. Either living or dead shoots may emanate allelochemicals that affect germination or growth at their vicinity. Compared with shoots, allelochemicals in roots have been less studied. Many seeds, fruits, and other dispersal units contain inhibitors of germination or growth that belong to widely diversified chemical groups. Examination of allelopathy through the study of seed germination or early growth of seedlings in response to specific allelochemicals or to plant extracts was often assessed under laboratory conditions in petri dishes. Therefore an ecologically meaningful evaluation of allelopathy through the study of the dose-response effects of allelochemicals on germinating seeds should include tests simulating natural conditions, particularly in soils.