Regeneration 



195 



R 



a limited growth (see Fig. 38), are directed 

 upward, and have polyps on their upper 

 side. The parts which grow down (Fig. 

 37) have no polyps, but attach themselves 

 like true roots to solid bodies. Thus the 

 changed position of the stem alone, with- 

 out any operation, suffices to transform 

 the lateral branches, whose growth is 

 limited, into roots with unlimited growth. 

 The lateral branches on the upper side of 

 the stem do not undergo such a transfor- 

 mation into roots except in the immediate 

 surroundings of the place where a new stem 

 arises. It seems that the formation of a 

 new stem also causes an excessive growth 

 of roots, possibly because the formation of 

 new branches causes the removal of sub- 

 stances which naturally inhibit the forma- 

 tion of roots. If a piece from the stem be 

 put vertically into the water with top down- 

 ward, the uppermost point may continue 

 to grow as a stem, while the lowest point 

 may give rise to roots. In this case, there- 

 fore, a change in the orientation of organs 

 has the effect of changing the character 

 of organs. 



There are only two ways by which we 

 can account for these influences of gravi- 



