A comparative study has been made of the geoelectric effect in Helianthus hypocotyls and Zea coleoptiles using two electrode systems. With the static-drop electrode system a potential difference developed between the upper and lower surfaces of the shoots immediately after they were turned into the horizontal position. The lower surface of the shoot became positively charged with respect to the upper surface. In non-decapitated shoots this potential difference continued to increase for at least 20 min, whereas in decapitated shoots no further increase occurred after about 10 min from the moment of reorientation. In contrast, with a flowing-solution electrode system no potential difference developed in non-decapitated shoots until about 12 min after they were placed in the horizontal position. Thereafter the lower surface became increasingly positively charged with respect to the upper surface for at least a further 12 min. In decapitated shoots there was no tendency whatsoever for the lower surface of the horizontal shoot to become positively charged with respect to the upper surface, even after 25 min in the horizontal position. The static-drop electrode system has an inherent sensitivity to reorientation in a gravitational field; a potential difference develops immediately after reorientation, and increases to a maximum value within the first 10 min of reorientation, regardless of whether or not the electrodes are in contact with plant tissue. The continued increase in the potential difference measured across the shoots with the static-drop electrode system, and the entire development of the potential difference measured with the flowing-solution electrode system, are both dependent upon the shoot apex being intact. These facts have enabled us to show that the electro-potential difference measured across horizontally placed non-decapitated tissues with the static-drop electrode system is the resultant of two distinct processes: (a) an immediate, purely physical electrical effect generated in the electrodes themselves, and (b) a delayed geoelectric effect which arises solely in the living tissues of the shoot and which is dependent upon the apex of the shoot being intact.