There remains now the important question of the physiological change induced on the lower side of the horizontally laid shoot. The physiological reaction of two sides of the organ must be different, since the upper side exhibits contraction and the lower side expansion. It may be urged that the effect of one of the two sides might result from the passive yielding to the definite reaction induced on the opposite side. Investigation by the electric method enables us, however, to discriminate the two reactions from each other, since the electric response characteristic of the induced physiological change takes place in the organ, even under condition of restraint by which movement is prevented. We shall therefore investigate the geo-electrical reaction on the lower side of the securely held organ, and find out whether the induced electric change undergoes any variation in different layers from below upwards. There are two different ways in which the electric explorations of the lower side of the organ may be carried out. In the first method, the probe is introduced from below, and successive readings for geo-electric response taken as the probe enters the organ by successive steps. It is understood that the true geotropic effect is found from difference of galvanometer readings in vertical and horizontal positions. In the second method, the probe is introduced from above, and successive readings for the response taken for different positions of the probe as it enters the organ from the upper side and comes out ultimately at the lower side. This I shall call the METHOD OF TRANSVERSE PERFORATION. The intrusion of the probe on the upper side gives, as we have seen, increasing negative deflection of the galvanometer which reaches a maximum at the perceptive layer. Passage of the probe to still greater depths give deflections which decline to zero. But when the probe comes within the influence of the perceptive layer of the under side, the electric indication, as we shall presently find, undergoes a reversal. ELECTRIC EXPLORATION OF THE LOWER SIDE OF THE ORGAN. I shall first describe the results obtained from the first method, the probe entering the organ from the lower side.