Considering the widely separated position in the vegetable series of the several above-named genera, we may conclude that the tips of the radicles of all, or almost all, plants are similarly sensitive, and transmit an influence causing the upper part to bend. With respect to the tips of the secondary radicles, those of Vicia faba, Pisum sativum, and Zea mays were alone observed, and they were found similarly sensitive. In order that these movements should be properly displayed, it appears necessary that the radicles should grow at their normal rate. If subjected to a high temperature and made to grow rapidly, the tips seem either to lose their sensitiveness, or the upper part to lose the power of bending. So it appears to be if they grow very slowly from not being vigorous, or from being kept at too low a temperature; also when they are forced to germinate in the middle of the winter. The curvature of the radicle sometimes occurs within from 6 to 8 hours after the tip has been irritated, and almost always within 24 h., excepting in the case of the massive radicles of Æsculus. The curvature often amounts to a rectangle,—that is, the terminal part bends upwards until the tip, which is but little curved, projects almost horizontally. Occasionally the tip, from the continued irritation of the attached object, continues to bend up until it forms a hook with the point directed towards the zenith, or a loop, or even a spire. After a time the radicle apparently becomes accustomed to the irritation, as occurs in the case of tendrils, for it again grows downwards, although the bit of card or other object may remain attached to the tip. It is evident that a small object attached to the free point of a vertically suspended radicle can offer no mechanical resistance to its growth as a whole, for the object is carried downwards as the radicle elongates, or upwards as the radicle curves upwards. Nor can the growth of the tip itself be mechanically checked by an object attached to it by gum-water, which remains all the time perfectly soft. The weight of the object, though quite insignificant, is opposed to the upward curvature. We may therefore conclude that it is the irritation due to contact which excites the movement. The contact, however, must be prolonged, for the tips of 15 radicles were rubbed for a short time, and this did not cause them to bend. Here then we have a case of specialised sensibility, like that of the glands of Drosera; for these are exquisitely sensitive to the slightest pressure if prolonged, but not to two or three rough touches.