Factors in Regeneration 337 



This retardation occurs irrespective of the region of the stem from 

 which the pieces were taken, and is due solely to the small size of 

 the pieces. 



Medium size pieces (with 10 to 15 lateral branches) regenerate 

 polyps at all the cut ends, including oral and basal ends, in approx- 

 imately the same time. Ligating the distal end or ends acceler- 

 ates basal regeneration. Ligating the distal end of small pieces 

 taken from the distal region of a stem, does not however accelerate 

 basal regeneration, because the coenosarc withdraws from the 

 distal end and the ligature does not affect it. When the single 

 lateral branch of small pieces (Experiment 9) was ligated the 

 rate of development was uninfluenced. Regeneration on small 

 old (basal) pieces taken from large stems, is very slow; it may 

 take six or seven days before polyps appear. 



Embedding inverted stems in sand and to a less degree suspend- 

 mg them, stmiulates the early formation of heteromorphic polyps, 

 but the rate of development at other cut ends was not at all or but 

 slightly affected. Lack of oxygen or low temperature or contact 

 with a solid body or greatly diluted or slightly concentrated sea- 

 water retards the development of the first formed polyps. In the 

 meantime the stems become more or less acclimatized to the new 

 conditions and polyps thereafter are regenerated at a normal 

 rate. Injuries of various kinds, such as lacerating and slitting 

 the stems in many places or disintegration of coenosarc in some 

 of the lateral branches, does not retard regeneration at the other 

 cut ends. All efforts to accelerate the normal period of regenera- 

 tion in less than two days, failed. 



EFFECTS OF GRAVITY^^ 



Experiment ij. A series of stems were suspended vertically 

 in a dish of water, some with the distal ends pointing upward 

 (toward the zenith), the "erect" stems; others in the contrary 

 direction, the "inverted" stems. The controls were placed hori- 



'"Loeb ('91) believed that gravity and light were the external factors that determined the kind and 

 direction of growth. Also see Driesch ('99). 



