Site of action of trifluralin on germinating Cenchrus echinatus LStudies were performed in pots and in field to know the capacity of germination of Cenchrus echinatus L. at different depths. In pots the seeds germinated from 1 to 11 cm and in the field from 1 to 9 cm in clay soil and from 1 to 10 cm in loamy soil. The germination of two or three seeds from the same fructescence was frequent. In two other tests the side of action of trifluralin at 0.84 kg/ha, in loamy soil, was studied. The herbicide showed activity on the meristematic zones of the root and coleoptile, inhibiting the growth of the shoot and root. The affected regions showed an increase in diameter.