Unlike almost all other higher plants, the germination of root parasites depends on receipt of a chemical signal. They germinate only in response to specific chemicals present in the rhizosphere of host plants. Orobanche species, like all other Orobanchaceae, is obligate root parasites that depend entirely on their hosts for all nutritional requirements. The embryo of root parasites is highly reduced, lacking cotyledons and a root cap. Root parasites exhibit two main life phases: the independent and the parasitic. When the seeds of root parasites are shed, they often show a period of dormancy, during which germination does not occur even under optimal conditions. This period is named after-ripening. Strigol is the first germination stimulant isolated for Striga. It also stimulates the germination of other root parasites. The only chemical that is practically used in infested fields for suicidal germination of root parasites is ethylene.