Biological Studies on Corymorpha. 



411 



of these organisms, must be similarly satisfactory for all. The 

 following characteristics of the geotropism of Corymorpha appear 

 to find no adequate explanation in existing theories. 



Suppose a Corymorpha stem (Fig. 2) to be cut at x into two 

 segments, A and B. Now, at whatever point A be supported 

 above the proximal end, the latter will seek the center of the earth. 

 On the other hand, at whatever point B be supported, its distal 



Fig. 2. 

 Diagram of stem, to illustrate geotropism. 



end (cut at the same level as the proximal end of A) is strongly 

 negatively geotropic. If the cut were made at x^, the shaded por- 

 tion which, as a part of B would have been negatively geotropic, 

 would now appear to be positively geotropic. I say "appear to 

 be," for while the negative response is due to a change in the 

 turgidity of the axial cells, the positive response may not be truly 

 geotropic, but may mark an unresponsive period in the axial 



