The series of experiments that Vöchting has carried out on the regeneration of the higher plants are so much more complete than all previous experiments, and his analysis of the problems concerning the factors that influence regeneration is so much more exact than any other attempts in this direction, that we may profitably confine our attention largely to his results. Many of his experiments were made with young twigs or shoots of the willow (salix), which, after the removal of the leaves, were suspended in a glass jar containing air saturated with water. Under these circumstances the pieces produced new shoots from the buds (leaf-buds) that are present near the point at which the leaves were attached, and new roots, in part from root-buds, that are also present on the stem. If the piece is suspended in a vertical position with its _apex upward_ (Fig. 32, _A_), small swellings appear after three or four days near the lower, _i.e._ the basal, end of the piece. These break through quickly and grow out as roots. If a leaf-bud is present near the basal end of the piece, the first roots appear at the side of or under this; later others appear around the same region. The first roots to appear under these conditions come from pre-formed root rudiments, the others are, in part at least, new, adventitious roots. If the lower end of the cut is made through the lower part of a long internode, _i.e._ just _above_ a bud, the roots appear as a rule only near the cut-end, and few if any of the roots develop at the first bud above this region. In many cases there is formed over the basal cut-surface, in the region of the cambium, a thickening, or callus, and not infrequently from this also one or more roots may develop. The direction taken by the new roots is variable, being sometimes downward, sometimes more or less nearly at right angles to the stem. While these changes have been taking place at the base, the leaf-buds at the apical end have begun to develop. One, two, three, four, or even five of the higher buds begin to elongate, the number and extent of development depending on the length of the piece. The topmost or apical bud grows fastest, and the others grow in the order of their position. In the region below the lowest bud that develops there may be one or more buds that do not grow; but if the piece is cut in two just above these buds, they will then grow out. [Illustration: FIG. 32.--After Vöchting. _A._ Piece of willow cut off in July, suspended in moist atmosphere with apex upward. _B._ Older piece of willow (cut off in March) suspended in moist atmosphere with apex downward. _C._ Piece of willow with a ring removed from middle. Apex upward. _D._ Piece of root of _Populus dilatata_. Basal end upward. Shoots from basal callus. _E._ Piece of root of same with two rings removed. New shoots develop from basal callus, and from basal end of each ring.]