FuRTHER INVESTIGATIONS ON HELIOTROPISM 108 
Til 
1. I have endeavored to find other animals in which helio- 
tropic curvatures are formed only in the growing parts. 
These efforts have been successful in the Hydroids. Stems of 
Sertularia (polyzonias ?) were cut off near the root and fixed 
in the sand in an inverted position, so that the cut end was 
directed upward. The stems were placed near a window 
through which the light fell obliquely and from above. The 
animals began to regenerate; new polyp-bearing stems grew 
from the cut end as well as new roots ;* but while the new 
stems grew upward and toward the window, the roots grew 
downward and toward the room side. The polyp-bearing 
shoots are positively, the roots negatively, heliotropic. That 
the negatively heliotropic elements were true roots was 
proved by the fact that when brought in contact with a solid 
body they attached themselves to it and continued to grow 
over its surface in close contact with it. They could be 
loosened from their attachments only by force. The polyp- 
bearing stems do not possess this kind of contact-irritability. 
The heliotropic phenomena will be readily understood by the 
aid of Figs. 13, 14, and 15: ab is the old stem, 6 the cut 
end; the stem is fixed in the sand to the point ac. From the 
cut end b arise newly formed roots W,, which bend down- 
ward away from the light and toward the room side of the 
aquarium. The new polyp-bearing shoots S grow upward 
and toward the window. The arrow marks the direction of 
the rays of diffuse daylight in this experiment. 
2. In these experiments new growths occasionally sprang 
from the middle of the old stem, which, so far as their con- 
tact irritability was concerned, reacted as roots. Those 
tendrils which attached themselves to solid bodies were 
always negatively heliotropic. They grew downward and 
1 Which is of importance in the theory of organization. 
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