ORGANIZATION AND GROWTH 



199 



orientation of Antennularia toward the center of the earth 

 are not exhausted by what has been said in the foregoing. 

 It is possible to cause the growing tip of the stem to cease 

 its growth and develop into a root. This is done by invert- 

 ing the tip. I cut long pieces from the stems of Antennu- 

 larise and hung them vertically 

 in the aquarium, but in an 

 inverted position. A rapidly 

 growing stem was formed at 

 the upper that is to say, the 

 basal end. When it had 

 attained a certain height, I 

 turned the whole animal about 

 a horizontal axis through an 

 angle of 180. Not in a single 

 instance did the tips of the 

 stems bend upward as the 

 negatively geotropic parts of 

 plants usually do under the 

 same conditions but they 

 ceased to grow and one or more 

 roots formed at their tips. 



Fig. 49 shows a stem at the 

 end of such an experiment ; 

 ab is the piece of stem upon 

 which the experiment was 

 started. It was at first fixed 



in an inverted position, so that the basal end b was directed 

 upward, and the apical end downward. The new stem be 

 sprang from the basal extremity, grew vertically upward, 

 and gave rise to lateral branches which were directed slightly 

 upward and carried polyps upon their upper surfaces. The 

 roots T^j-formed at 6, at the base of the new stem, as was usually 

 the case when the old stem did not stand entirely vertical. 



