214 STUDIES IN GENERAL PHYSIOLOGY 



space is also of importance for its organization. For it 

 is possible to control organization in Tubularia by contact 

 stimuli to such an extent that by their help we can pre- 

 scribe in a large measure whether a root or a polyp shall 

 grow from the aboral cut end of a Tubularian. If the 

 aboral end of a piece of Tubularian stem is surrounded by 

 water, so that it does not rub against the surface of 

 solid bodies, almost without exception a polyp is formed 

 upon it instead of a root; heteroraorphosis occurs instead 

 of regeneration. If, however, the same end is brought into 

 permanent contact with the surface of a solid body if, 

 for example, the stem is laid horizontally upon the bottom 

 of the vessel a root is often formed. But to accomplish this 

 it is necessary to keep the dish quiet, and care must be taken 

 that the same side of the stem remains in contact with the 

 solid body ; otherwise it does not attach itself. If the stem 

 does not attach itself, a polyp is soon formed, just as a polyp 

 is formed at the tip of a Tubularian root which has been 

 freed from the bottom of the vessel, as soon as it is sur- 

 rounded by water. Of course, it is in every case necessary 

 that the general conditions of growth of the animal, which 

 we shall discuss later, be fulfilled. I remember that only 

 once in hundreds of individual experiments did I see a root 

 grow without contact with a solid body. 1 But a factor came 

 into play here which still brings this case under the 

 general grouping. I had cut a section from the stem of 

 a Tubularian, and had laid it horizontally upon the bot- 

 tom of a glass vessel. A root sprang from the aboral end 

 which attached itself to the bottom of the vessel. Simul- 

 taneously with this root arose a second, which curved up- 

 ward somewhat, and which continued to grow as a root with- 

 out contact with a solid body. The exception was probably 



i In recent experiments on Tubularia crocea I have frequently observed the for- 

 mation of roots at the aboral end, even if the latter was not in contact with a solid 

 body. [1903] 



