208 STUDIES IN GENERAL PHYSIOLOGY 



has thus far been the lower end of the piece, while those substances 

 leading to the formation of stems will collect at the upper end. 

 Since their flow is stopped here, which would have been impossible 

 in the uninjured plaut, they give rise to the roots and stems at the 

 corresponding ends. In a piece of leaf capable of regeneration both 

 kinds of formative substances will be moving simultaneously 

 toward the basal end to flow toward the stem; stopped 

 by the cut surface, they collect there to form stems 

 and roots simultaneously. (P. 470.) 



a. Finally, "the different formative substances are 

 produced only in limited quantities" (p. -468). 



Corresponding to this theory we assume that 

 there are present in the stems of a Tubularian 

 ~d specific substances for the formation of polyps 

 which gather at both cut ends and thus bring 

 about the formation of polyps. These substances 

 must, however, cctcris paribus, collect more 

 quickly, or in sufficient amounts, sooner at the 

 oral than at the aboral cut end; and the cause of 

 this difference is to be determined by experiment. 

 3. It might at first be thought that the specific 

 substances necessary for the formation of polyps exist from 

 the beginning in greater amount at the oral end of a Tubu- 

 larian stem than at the aboral, and that a polyp is, in conse- 

 quence, formed more quickly at the oral than at the aboral 

 end. To ascertain whether this be true I amputated the 

 root and the polyp of Tubularians and cut the remaining 

 stem ab (Fig. 53) in half by a transverse incision between c 

 and d. All four cut ends were surrounded by water. If 

 now the substance necessary for the formation of polyps 

 were present in larger amounts in the oral half ac than in 

 the aboral piece bd, the former should form polyps sooner 

 than the latter. Yet polyps were formed at about the same 

 time upon both pieces, only the oral cut ends a and d 

 developed polyps much sooner than c and 6. I have already 



