136 STUDIES IN GENERAL PHYSIOLOGY 



which they are brought in contact, no matter how long one 

 may wait; while, on the other hand, this reaction is always 

 obtained with certainty in growing roots. I have also 

 assured myself of the fact that when adventitious roots are 

 brought in contact with the wall of a beaker, they imme- 

 diately attach themselves to it, and grow on its surface. 



11. As soon as a root comes in contact with a solid body, 

 it grows rapidly in length, and in a few days exceeds the 

 length of other newly formed and equally long roots, which 

 are prevented from contact with solid bodies. 1 



The attachment of the root to a solid body influences form 

 in a second direction. While we observed above that new 

 stems grow from the upper surface of a root when it is sur- 

 rounded on all sides by water, we find, when the root is 

 attached to a solid substratum, that the stems arise from that 

 surface of the root which lies opposite the solid body. In 

 their further development these stems also grow only straight 

 upward, though not entirely vertically. 



12. I have observed in the roots of Aglaophenia a phe- 

 nomenon relative to growth which has thus far been known 

 only in plants. 



The longitudinal growth of the root is confined to a nar- 

 row region situated near the tip (while no longitudinal 

 growth occurs in the remaining portions of the root). This 

 could be shown in the following way: I permitted the roots 

 of Aglaophenia to attach themselves to a slide and grow 

 upon it. A slight bulging out soon occurred just behind the 

 tips the beginning of a new stem, which on the next day 

 reached a length of |mm. and soon thereafter bore polyps. 

 I marked the position of the beginning stem on the glass, 

 by etching a line into the glass. The position of this new 



i DAL YELL observed in Sertularia halecina that new growths occur which 

 adhere to other solid bodies and thereby become abnormally long. "These com- 

 ing in contact with a solid surface have a tendency to adhere and to extend in 

 irregular prolongations surpassing the natural increment," Bare and Remarkable 

 Animals of Scotland (London, 1847), p. 165. 



