DYNAMICS OF REGENERATIVE PROCESSES 207 



consider it as established experimentally that the conditions which de- 

 termine the morphological polarity are due to something of the nature 

 of a current inside of the Tubularian. The mysterious morphological 

 polarity is thus reduced to a polarity which can be expressed in physical 

 or physicochemical terms. We see that this result differs in one point 

 from Sachs's hypothesis. The latter includes the effect of specific sub- 

 stances, while this condition does not appear in the results of our experi- 

 ments. It is, however, hardly necessary to state that our experiments by 

 no means exclude this possibility. I have discussed the case of regen- 

 eration in Tubularians at some length, not only because it is well known 

 to me through my own experiments, but also because on account of 

 its simplicity, it lends itself better to a reduction of dynamically 

 unintelligible morphological data to the more rationally expressible physi- 

 cal or physicochemical conditions. 



Osterhout and I tried to test the effects of a ligature on plants, espe- 

 cially on willow twigs. As we have already stated, a piece cut out from 

 a willow twig forms roots first at the basal and shoots at the apical end. 

 The process of regeneration in this case differs in several essential fea- 

 tures from that in Tubularians. The formation of the new organs 

 occurs in the willow twig not at the cut end but at the anlage of the 

 roots and shoots, both of which exist here normally. All that the opera- 

 tion does in this case is to cause the anlage of roots which would never 

 have developed now to grow out into roots. The reader should reahze 

 that the anlage of the roots which begin to grow in consequence of the 

 cutting off of the twig is not injured by the operation and is often far , 

 removed from the wound. The idea that this anlage grows out be- 

 cause the sap which would otherwise flow downwards is now blocked || 

 by the cut, and becomes available for the anlage of the roots, looks very' 

 plausible in the light of the actual facts. As part of the sap flow can 

 be suppressed by a tight ligature around the rind of a stem, Osterhout 

 and I tried the experiment of hgaturing a number of willow twigs in 

 the middle. The result was that a ligature caused the root anlage 

 above it and the shoots below it to develop, which without the ligature 

 would not have developed. In the case of the willow, we are also deal- 

 ing with a flow of material through conductive tissue, i.e. tissue through 

 which nutritive material is conducted. 



3. Regeneration in an Actinian (Cerianihus membranaceus) 



The phenomena of regeneration in Cerianthus can be easily under- 

 stood from the experiments on Tubularians, if we imagine the body 

 wall of Cerianthus to consist of a series of longitudinal elements which 



