KEGENERATION U 



stock and have fallen to the ground. If, finally, a torn-ofF poljq^-stalk 

 (of Tubularia) falls to the ground with the wrong side up, the end 

 which is now the lower will send out roots, and the end now upper- 

 most will give ofi" a new head. This also appears to us adaptive, and 

 does not surprise us, since we have been long accustomed to recognize 

 that what is adapted to an end will realize this if it be possible at all. 

 Think again of the innumerable adaptations in colour and form which 

 we discussed in the earlier lectures. I hope later to be able to show 

 in more detail how it comes to pass that necessity gives rise to 

 adaptation. In regard to the case of the polyps, we can understand 

 that, as far as a high degree of regeneration and budding was possible 

 in these animals at all, it could not but be developed. Regeneration 

 and budding complete each other in this case, for the former brings 

 about in the individual ' person ' what the latter does in the colon}^, 

 namely, a Restitutio in integrum. It is readily intelligible that the 

 former was not difficult to establish where the latter — the capacity 

 of budding — was alreadj?- in existence. 



It seems at first sight very striking that the higher plants, which 

 all depend upon budding, and which form plant-colonies (corms) 

 in the same sense as the polyps form animal-colonies, only possess 

 the faculty of true regeneration in a very low degree, although they 

 are extremely liable to injury. 



We see from this that the two capacities are not co-extensive, 

 that germ -plasm may be contained in numerous cells of the body 

 in a latent state, and yet that regeneration of each and every detailed 

 defect may not be possible. This is the case in the higher plants 

 in regard to most of their parts. A leaf in which a hole has been 

 cut does not close the hole with new cell-material ; a fern frond from 

 which some of the pinnules have been cut ofi" does not grow new ones, 

 but remains mutilated. Even leaves which, if laid on damp earth, 

 readily give off" buds which grow to new plants, as the Begonias do, 

 do not replace a j)iece cut out of the leaf ; they are not at all adapted 

 to regeneration. 



From the standpoint of utility this is readily intelligible. It 

 was, so to speak, not worth Nature's while to make such adaptations 

 in the case of leaves or blossoms, partly because these are very 

 transient structures, and partly because they are rapidly and easily 

 replaceable by the development of others of the same kind. More- 

 over, the leaf in which we have cut a hole continues to function, 

 but the polyp whose mouth and tentacles we have cut off could no 

 longer take nourishment unless it were adapted for regeneration. 

 But that this adaptation could have been made in the case of plants 



