Regeneration 



195 



Fig. 38 



-Ja 



y\ 



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

 upward, and have polyps on their upper 

 side. The parts which grow down (Fi^. 

 2,7) have no polyps, but attach themselves 

 like true roots to soHd 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 brancli^^s 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- 



