104 STUDIES IN GENERAL PHYSIOLOGY 
toward the room side, and remained free of Hydranths. (See 
Fig. 13, W,.) 
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 
growing 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 Algz ?), the color of the new growths is a light 
yellow. The growing elements curved themselves 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 the 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 
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