634 STUDIES IN GENEEAL PHYSIOLOGY 



it had flowed back to the point e. This was on the third 

 day of the experiment. I have however noticed that the stem 

 can send out stolons in different directions sinmltaneously. 



The hereditary arrangement of organs in Hydroids is 

 unequivocally determined by external circumstances, espe- 

 cially contact. A germ or larva of a Hydroid will form 

 roots 011 one side only, namely the side where it touches 

 solid bodies: 011 the opposite side where it touches sea- 

 water it will produce polyps or stems. The negative stere- 

 otropism of the latter or their positive heliotropism as in the 

 case of Eudendrium will cause them to continue growing 

 away from the solid body into the sea-water. Weismann is 

 therefore wrong in assuming that the hereditary arrange- 

 ment of the organs in Hydroids is due to a definite arrange- 

 ment of the elements in the germ. 



II 



What is the character of the physical or physiological 

 processes which underlie the transformation of organs ? 

 Such complicated formations as the polyp in Campanularia 

 are only possible if certain of the constituents are solid. 

 The transformation of such a polyp into the more shapeless 

 flowing or creeping material of the stem can only be due to 

 a liquefaction of these solid constituents. It is moreover 

 certain that contact with sea-water favors the formation of 

 polyps with its more solid elements, while the contact with 

 solid bodies favors the formation of the more fluid material 

 of the stem or stolon. Hence it seems as if the nature of 

 contact in this case determined the state of matter of certain 

 colloids in the Campanularia. 1 Although I had observed the 

 influence of the nature of contact upon these phenomena for 

 many years I had not been able to form any definite idea of 



1 1 do not need to mention especially that the periderm does not participate in 

 these liquefactions. 



