104 



STUDIES IN GENERAL PHYSIOLOGY 



toward the room side, and remained free of Hydraiitbs. (See 

 Fig. 13, W a .) 



On the other hand, I saw also new polyp-bearing stems 

 arise from the old stems, although much less frequently; 

 these grew in the opposite direction, namely upward. 



3. That in the case of Sertularia it is, indeed, only the 

 (jroirii/i/ parts which produce the heliotropic curvatures is 



FIG. 13 



FIG. 14 



FIG. 15 



shown by the following experiment. The growing tips were 

 cut off a large number of Sertularia stems. The stems began 

 to grow, and in the course of a few days sent out new sprouts. 

 The new growth is strikingly different in color from the old 

 stem ; while the latter is rather brown (from having been 

 covered by Algae ?), the color of the new growths is a light 

 yellow. The growing elements curved thcmselres until the 

 growing points lay in the direction of the rays of light and 

 then continued to grow in this direction. During all this 

 time no change in the orientation of tJte old stem occurred, 

 nor did any take place in other uninjured stems, in which no 

 linear growth occurred during this time. 



How far gravity played a role in these experiments I was 



