HETEROMORPHOSIS 125 
solid body and became a root; however, when contact with 
the wall of the aquarium was broken so that water sur- 
rounded the root on all sides, a polyp was formed also at the 
end of the root. In my further experiments I shall try to 
find conditions under which the animal will form roots at 
both poles with just as great certainty as it now forms heads. 
From the experiments thus far discussed, I can only con- 
clude that the formation of polyps in Tubularia mesembry- 
anthemum can be brought about much more easily than the 
formation of roots. 
Ill THE LIFE-PHENOMENA OF THE ORAL POLE OF TUBU- 
LARIA MESEMBRYANTHEMUM 
Doubt might arise as to whether the two heads of a bioral 
Tubularian manifest the same life-phenomena; as to whether 
the two morphologically equal poles are also identical physio- 
logically. I shall show that this is, indeed, the case, and in 
doing so shall dwell a little more upon the differences in the 
irritability of stem and root. 
1. The stem and root of Tubularia mesembryanthemum 
have an entirely different contact-irritability. If the root is 
brought in contact with a solid body, it attaches itself to it, 
and in its further growth remains closely attached to the sur- 
face of the solid. If an attempt is made to lift the stem 
from the solid body, it tears off close to the root, the latter 
remaining attached to the base upon which it grew. The 
polyp has exactly the opposite irritability. When the polyp 
comes in contact with a solid body—for example, when the 
stem lies horizontally upon the bottom of the aquarium —it 
soon grows away from it. The growing region of the stem 
(which is situated close behind the polyp) becomes convex 
against the solid substratum. 
This (stereotropic) bending occurs only in the growing 
part of the stem, and persists when growth has ceased, just 
Digitized by Microsoft® 
