RELATIVE STABILITY OF LIVING MATTER 329 



eye or the antenna should appear, but as many eyes were regener- 

 ated in the dark as in the light. It was found, however, by both 

 Herbst and Morgan independently, that "when the end only of 

 the eyestalk is cut off an eye regenerates, but when the eyestalk 

 is cut off at the base an antenna regenerates." 1 



Effect of gravity upon regeneration. The effect of gravity upon 

 regeneration in plants is pronounced, 2 but only one case is known 

 of its influence upon regeneration in animals. This is the case of 

 the hydroid Antennularia antennina? 



This animal, however, has many of the characteristics of the 

 plant, for it lives attached by a kind of root to the bottom of 

 the sea, and its general form is that of a branching stem, like a 

 typical plant. All experiments show that regeneration in this 

 form is always with reference to gravity, much as in the case of 

 plants. Whatever the position of the piece, the new growth is 

 upward from the most elevated part, whether basal or apical, and 

 downward from the lower extremity and from the base of the 

 new growth (see Fig. 41). 



The effect of gravity upon regeneration in plants may be 

 briefly summarized as follows : 4 



1. If a piece of stem of the willow be suspended with its 

 apex upward, in three or four days roots will spring from small 

 swellings at the basal 5 end, and three or four buds will arise at 

 the apical 5 end, the one at the extreme tip coming first and grow- 

 ing fastest, others in regular decreasing order (see Fig. 26, A). 



2. If the piece is long the lower buds will not start, but if it 

 should be cut in two pieces, or if a ring of bark should be cut from 

 the middle, each would behave as already described, showing 

 that any point on the stem may throw out either shoots or roots, 

 according to its position with reference to the cut and to gravity. 



3. These new growths generally arise from preexisting buds 

 if the piece is young, but they may arise from regions entirely 

 destitute of preexisting buds. The writer knew a red maple tree 



1 Morgan, Regeneration, p. 30. 2 Ibid. pp. 71-80. 8 Ibid. pp. 30-32. 



4 The pieces experimented upon were suspended in moist atmosphere. 



* In all these explanations "basal" means the end that was down whe 

 plant was in its normal position, whatever its position during the exper 

 "Apical" refers to the end farthest from the base in nature. 



