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 



