It was shown in the last chapter that the stolons or runners of certain plants circumnutate largely, and that this movement apparently aids them in finding a passage between the crowded stems of adjoining plants. If it could be proved that their movements had been modified and increased for this special purpose, they ought to have been included in the present chapter; but as the amplitude of their revolutions is not so conspicuously different from that of ordinary plants, as in the case of climbers, we have no evidence on this head. We encounter the same doubt in the case of some plants which bury their pods in the ground. This burying process is certainly favoured by the circumnutation of the flower-peduncle; but we do not know whether it has been increased for this special purpose. EPINASTY—HYPONASTY. The term epinasty is used by De Vries[2] to express greater longitudinal growth along the upper than along the lower side of a part, which is thus caused to bend downwards; and hyponasty is used for the reversed process, by which the part is made to bend upwards. These actions come into play so frequently that the use of the above two terms is highly convenient. The movements thus induced result from a modified form of circumnutation; for, as we shall immediately see, an organ under the influence of epinasty does not generally move in a straight line downwards, or under that of hyponasty upwards, but oscillates up and down with some lateral movement: it moves, however, in a preponderant manner in one direction. This shows that there is some growth on all sides of the part, but more on the upper side in the case of epinasty, and more on the lower side in that of hyponasty, than on the other sides. At the same time there may be in addition, as De Vries insists, increased growth on one side due to geotropism, and on another side due to heliotropism; and thus the effects of epinasty or of hyponasty may be either increased or lessened. [2] ‘Arbeiten des Bot. Inst., in Würzburg,’ Heft ii. 1872, p. 223. De Vries has slightly modified (p. 252) the meaning of the above two terms as first used by Schimper, and they have been adopted in this sense by Sachs. He who likes, may speak of ordinary circumnutation as being combined with epinasty, hyponasty, the effects of gravitation, light, etc.; but it seems to us, from reasons hereafter to be given, to be more correct to say that circumnutation is modified by these several agencies. We will therefore speak of circumnutation, which is always in progress, as modified by epinasty, hyponasty, geotropism, or other agencies, whether internal or external.