Although the experiments with pieces of young willow-twigs may seem to show that gravity is not a factor in regulating the development of the new parts, the results show in reality only that internal factors have a preponderating influence. By means of another series of experiments it can be shown that gravity does have an influence on the production of the new parts. It is evident that in order to test the action of gravity, pieces must be placed in different positions in relation to the vertical. It will be found, if this is done, that different results are obtained according to the angle that the piece makes with the vertical. If a piece is suspended in a moist atmosphere, with its _apical end upward_, the smaller the angle that the piece makes with the vertical so much the more are the leaf-buds that develop confined to the upper part of the piece, and so much the more do they develop from all sides of the upper end; conversely, the greater the angle with the vertical, _i.e._ the more nearly horizontal the position of the piece, so much the more are the leaf-buds that develop found along the _upper side_ of the apical end (as well as around the end). If the piece is placed in a horizontal position, the leaf-buds develop not only around the apex, but they develop along the entire length of the upper surface, best, however, near the apical end. If similar pieces are suspended in oblique positions, with the _basal end upward_, different results are obtained. In the preceding experiment the polarity of the piece and gravity act together, while in this experiment their action is opposed. Although there is a great amount of variability in the results, yet the action of gravity is found to have less influence on the result than has the inner polarity, and the influence of the latter is so much greater that the action of gravity is hardly noticeable. The roots do not show as markedly the influence of gravity as do the leaf-buds, yet Vöchting has found that the position in which they appear varies with the position of the piece with respect to the vertical. [Illustration: FIG. 34.--After Vöchting. _A._ End of a piece of _Heterocentron diversifolium_. Apex downward. _B._ Piece of same bent and suspended “with concave-side upward.” _C._ Piece of a stem of _Salix viminalis_. Apex upward. A piece of the side has been lifted up and two wedges inserted.]