2/2 REGENERATION 



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 devel- 

 opment 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 onJy the more api- 

 cally 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 ten- 

 sion 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 reestablishing 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 regener- 

 ates a circle of tentacles near the region of union, and each may pro- 

 duce 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 con- 

 dition 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. 



It is probable, in this case, that the larger component has acted 

 on the smaller one, so that its polarity is changed and becomes like 



