HETEROMORPHOSIS 185 
the new stem from the upper portions. The new stems grew 
upward, the roots downward. I have seen such new stems 
arise, not only from the main stem and the main roots, but 
also from the adventitious roots. Here also the new stems 
always grew upward. Finally, I have seen new stems, which 
also grew upward, arise from stems lying horizontally. 
When, however, I cut off the tip from stems lying hori- 
zontally, and regeneration occurred without heteromorphosis 
or deformity of any kind, the new tip showed, so far as 
my present experience goes, no tendency to bend upward. 
9. All newly formed stems arose from the upper surface of 
the stem or root (see Fig. 19, s), it mattered not whether they 
grew upon the main stem or upon the accessory roots. The 
accessory roots sprang from the lower surface of the stems 
when these lay horizontally. Whether all these phenomena 
are determined solely by gravity I shall attempt to decide 
by further experiment. 
10. That form of contact-irritability which I have called 
stereotropism plays an important réle in the growth of the 
root of Aglaophenia. When the roots come in contact with 
asolid body, they attach themselves to it (by means of a 
secretion?) and grow along its surface. This attachment is 
a phenomenon of irritability which is called forth by contact 
with the solid body itself; for when the root is brought in 
contact with a solid body, it does not immediately stick to it, 
but only after contact has lasted for some time (often as long 
as twenty-four hours). Only the growing part (tip) of the 
root is able to fasten itself to the surface of aslide. The 
root adheres so firmly to the solid body that it is impossible 
to separate the two by traction; the root tears before it can 
be pulled from the solid body. I have not as yet observed 
the branches of Aglaophenia bend away from a solid body. 
Yet I have proved with certainty that growing branches car- 
rying polyps never attach themselves to a solid body with 
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