634 STUDIES IN GENERAL 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 simultaneously. 
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 on one side only, namely the side where it touches 
solid bodies: on 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.’’ Although I had observed the 
influence of the nature of contact upon these phenomena fur 
many years I had not been able to form any definite idea of 
1I do not need to mention especially that the periderm does not participate in 
these liquefactions. 
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