Investigation having shown that it is the tip of the radicle that is sensitive to geotropism in the members of such distinct families as the Leguminosæ, Malvaceæ, Cucurbitaceæ and Gramineæ, which may be represented by the Clover, Mallow, Gourd and Rye, we may justly infer that this character is common to the roots of most seedling-plants. Whilst a root is penetrating the ground, the tip must take the incipient step, as it has to determine the direction of the entire root. When, however, it is deflected by any subterranean obstacle, it is essential that a considerable length of the root should be able to bend, particularly as the tip itself grows slowly and bends but little, so that the proper downward course should be recovered. Immaterial as it would seem whether the entire growing part should be so sensitive to geotropism as to effect this movement, or that it should be brought about by an influence transmitted exclusively from the tip, we should, however, remember that it is the tip that is sensitive to the contact of hard objects, causing the radicle to bend away from them, thus directing it along certain lines in the soil where the least opposition interposes. It is again the tip that is alone sensitive, at least in some instances, to moisture, causing the radicle to bend towards its source. These last two kinds of sensitiveness conquer for a time the sensitiveness to geotropism, which, however, ultimately prevails. But the three kinds most often come into antagonism, first one prevailing, and then the other. It would, therefore, be an advantage, perhaps a necessity, for the interweighing and reconciling of these different kinds of sensitiveness, that they should all be localized in the same group of cells which have to transmit the command to the adjoining parts of the radicle, necessitating it to bend to or from the source of the irritation. Though generally believed by authors that the modification of the upper or lower surfaces of a radicle, whereby curvature is induced in the proper direction, is the direct result of gravitation, yet there can be no question from all that has been said that it is the tip alone that is acted on and that transmits some influence to the adjoining parts, causing them to curve in a downward manner. Gravity, it would seem, does not act in a more direct way on a radicle than it does on any lowly-organized animal, which moves away when it feels some weight or pressure.