Regeneration 



167 



are associated or identical with the substances which 

 cause geotropic curvature in the stem. 



These observations show that 

 the phenomena of correlation or 

 of the influence of the whole over 

 the parts is due to peculiarities of 

 circulation or the flow of sap ; and 

 that the isolation prevents the sap 

 from flowing away to other parts 

 of the plant. There is no need for 

 assuming the existence of a mys- 

 terious force which directs the piece 

 to grow into a whole. 



3. Phenomena of inhibition or correlation such as 

 we have described in Bryophyllum are not lacking in 

 the regeneration of animals, as experiments on Tubu- 

 lar ia show. 1 Tubularia mesembryanthemum (Fig. 21) 

 is a hydroid consisting of a long stem terminating at 



one end in a stolon 

 which attaches it- 

 self to solid bodies 

 such as rocks, at 

 the other end in a polyp. The writer found that if 

 we cut a piece from a stolon and suspend it in an aquar- 

 ium it forms as a rule a polyp at either end (Fig. 22), 



Fig. 21 



Fig. 22 



1 Loeb, J. ( Untersuchungen zur physiologischen Morphologie. I. 

 Heteromorphose. 1891. II. Organbildung und Wachsthum. Wurz- 

 burg, 1892. 



