due, as Vöchting tries to show, in part to the influence of gravity on the piece. Vöchting’s general conclusion is that “the force or forces that determine the _polar differences_ in the piece are most evident and most energetic in very young twigs; that this difference decreases with the age of the twig whose leaf-buds and root-buds become further developed. It is clear that the new roots of _young twigs_ could appear in corresponding number and strength in exactly the same regions in which they grow out from pre-formed buds of _a year-old twig_. Since this does not occur, and since the roots appear only near the base of young twigs, the explanation must be that the innate polar forces act more energetically in young twigs, and the buds that develop in the older twigs must arise in antagonism to the action of this force.” The polar difference between apex and base is present, nevertheless, as Vöchting’s experiments show, even in quite old pieces. [Illustration: FIG. 33.--After Vöchting. _A._ Internodal piece of _Begonia discolor_. Apex upward. _B._ Same with apex downward. _C._ Internodal piece of _Heterocentron diversifolium_. Apex upward. _D, E._ Pieces of leaf of _Heterocentron diversifolium_. Apex downward. _F._ Same with apex upward. _D, E, F._ Same planted in earth.] A series of experiments was carried out with the internodes of several plants in order to see if, in the absence of pre-formed buds, new buds would develop. The experiments were undertaken in order to ascertain whether the same polarity, exhibited by longer pieces, would be also found in internodal pieces. In most plants pieces of this kind do not produce new structures, but in _Heterocentron diversifolium_ an internode produces roots at its basal end without regard to the position of the piece (Fig. 33, _C_). Leaves do not appear on these pieces. On the other hand internodes of _Begonia discolor_ give the opposite result, as shown in Fig. 33, _A, B_. In this case leaf-buds appear at the apex of the internodal piece (Fig. 33, _A_), even when the apical end is downward (Fig. 33, _B_). From the bases of the new shoots roots may then develop, as also shown in the figure (Fig. 33, _B_). Vöchting concludes that the same polarity that is a characteristic feature of longer pieces is also present in internodal pieces. It is not necessary to separate completely portions of the stem in order to produce roots near one end and shoots near the other. If a ring, including the cambium layer, is cut from the piece, as indicated in Fig. 32, _C_, the part above and the part below act independently of each other, and each behaves as a separate piece. In various other ways the same result may be obtained, as by simply making an incision in the stem at one side, or by partially splitting off parts of the stem (Fig. 34, _C_).