HETEROMORPHOSIS 141 
stimuli in which not only the internal structural conditions, 
but these and the external stimuli together, determine the 
result, The external stimuli with which we deal here seem 
to be light and possibly gravity. 
3. The effect of light upon the formation of new polyps 
in Eudendrium is shown in an unmistakable way. When one 
compares the number of new polyps and branches formed 
upon the window side of the stem with those formed upon 
the room side, one finds that the number upon the window 
side is very much the larger. 
The branches are, moreover, positively heliotropic. I 
cut off a Eudendrium at its base, close above the root; a 
new polyp was formed upon the tip of the stump that 
remained. The stem then began to grow rapidly. The 
growing, apical portion of the stem bent toward the window 
side of the aquarium. That part of the stem which was not 
growing actively showed no heliotropic curvature. 
4. I have made a single observation which seems to indi- 
cate that currents in the water, if they are continued for 
some time and always in the same direction, can pro- 
duce curvatures in a growing Eudendrium stem. The anal 
opening of a large Ascidian was situated near a growing 
Eudendrium stem, so that the stream of water ejected by 
the Ascidian struck the Eudendrium. The growing part of 
the Eudendrium which was struck by the current of water 
bent so as to have its concave side directed toward the 
source of the current. The other stems of the same 
culture which had been subjected to otherwise similar treat- 
ment had all bent toward the source of light. This observa- 
tion also shows that the rheotropism of these Eudendrium 
stems—if we are, indeed, dealing with this phenomenon— 
is able to overcome and to veil their heliotropism. 
5. In a few cases in which contact had been especially 
close, roots were formed in the middle of the stem, where it 
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