When we consider what we have written, it is impossible not to be impressed with the resemblance between the movements of plants and many of the actions performed by the lower animals. With plants an astonishingly small stimulus suffices. One plant may be highly sensitive to the slightest continued pressure, while a closely-allied form just as highly sensitive to a slight momentary touch. The habit of moving at certain periods is inherited both by plants and animals; and other points of similitude have been specified. But the most striking resemblance is the localization of their sensitiveness, and the transmission of a stimulus from the exciting point to another, which consequently moves. Yet plants do not, of course, possess nerves or a central nervous system. May we not therefore infer, and wisely so, too, that with animals such structures but serve for the more perfect transmission of impressions, and for the more complete intercommunication of their several parts? No structure in plants seems more wonderful, as far as its functions are concerned, than the tip of the radicle. Lightly pressed or burnt or cut, it transmits an influence to the upper adjoining part, causing it to bend away from the affected side. But more surprising, however, is the fact that the tip can distinguish between a slightly harder and softer object, by which it is simultaneously pressed on opposite sides. Let the radicle be pressed by a similar object a little above the tip, and it will be noticed that the pressed part does not transmit any influence to the more distant parts, but bends abruptly towards the object. Perceiving the air to be moister on one side than the other, it likewise sends out an influence to the upper adjoining part, which deflects towards the source of the moisture. When excited by light, the neighboring part bends from the light; but when excited by gravitation, the same part bends towards the centre of gravity. In almost every instance the ultimate purpose or advantage of the several movements can be clearly perceived. Two, or perhaps more, of the exciting causes often act simultaneously on the tip, and one conquers the other, doubtless in accordance with its importance for the life of the plant. The course pursued by the radicle in penetrating the ground being determined by the tip, has acquired for it the diverse kinds of sensitiveness which it possesses; and it is hardly an exaggeration to assert that the tip of the radicle thus endowed, and having the power to direct the movements of the adjoining parts, acts like the brain of one of the lower animals, which organ, seated within the anterior end of the body, receives impressions from the sense-organs, and directs their several movements.