AbstractThe Tarahumara Indians of the north‐west Mexican Highland practice a method of using several weeds for food which are called “quelites”. These weeds play an important role in the Tarahumara diet and seem to be connected with maize‐cultivation in a special way.In bio‐assays with two quelites species,Bidens pilosasens. lat. (Cobblers' pegs) andLepidium virginicum(Pepper grass) and different cultivars of maize (Zea maysL.) it could be demonstrated that water extracts of leaves ofB. pilosaandL. virginicumcause a significant stimulation of seedling growth of maize. Different cultivars of maize showed no differences in being stimulated by extracts ofB. pilosa.This indicates an allelopathic potential of the two tested quelites species.Extracts of leaves of older plants ofB. pilosa(shortly before flowering) do not show this effect. Different water extracts of maize snowed an indifferent influence on germination and seedling growth ofB. pilosaandL. virginicum.Considering these results the practice of the Tarahumara Indians — leaving the quelites a certain amount of time among their maize and harvesting them after that — appears to be a stimulatory method for growing maize. The maize‐quelites double‐crop system seems to be highly tuned and may be understood as a result of a process of cultural learning among the T