It has been already pointed out that in a piece of a plant suspended in a moist atmosphere, the apical buds are those that first develop, and also grow faster than the others. The buds situated nearer the base may not even begin to develop, although they are at first as favorably situated, so far as external circumstances are concerned, as the uppermost ones. The roots appear first over the basal end, and those nearer the base grow faster than do those nearer the apex. There cannot be much doubt that the suppression of the basal buds and of the more apical roots is connected with the development of the apical buds and of the basal roots. This can be shown by cutting a piece in two, when some of the basal buds will grow into shoots and the apically situated root-buds, that are now on the base of one piece, will begin to grow. It seems to me this relation can be at least more fully grasped, if we look upon it as connected with some condition of tension in the living part. The tension can be thought of as existing throughout the softer, more plastic parts. As long as the apical bud is present at the end of a stem or branch, or even near the apex, it exerts on the parts lying proximal to it a pull, or tension, that holds the development of these parts in check; but if the apical bud is removed the tension is relaxed, and the chance for another bud developing is given. It may be asked, how can it be explained that only the more apically situated buds of a piece develop, rather than the basal ones, since with the removal of the piece from the plant the tension has been removed also. The only answer that can be made, so far as I can see, would be that from the apex of the plant to its base the tension is graded, being least at the apex and increasing as we pass to the base. Those buds will first develop that are in the region of least tension, and their development will hold in check the other buds by increasing or reëstablishing the tension on the lower parts of the piece. A new system is then established, like that in the normal plant. There are certain experiments with hydra that can, perhaps, be brought under the same point of view. When two long posterior pieces are united by their anterior cut-surfaces, each piece regenerates a circle of tentacles near the region of union, and each may produce a new head; or only one head, common to both pieces, develops at the side. Each piece has retained its individuality, which may be interpreted to mean that each piece has retained its original condition of tension. If, however, after a union of this kind one piece is cut off, as soon as the two have well united, near the place of union, so that it is relatively small as compared with the other component, it may produce a head at its exposed basal end, and neither heads nor tentacles may develop at the place of union of the pieces.