134 STUDIES IN GENERAL PHYSIOLOGY 
lost organs occurred—a fact probably not entirely due to 
lack of light. 
7. The roots were characterized by a distinct kind of 
contact-irritability and by a tendency to bend downward, 
which I shall now discuss. 
When a root was formed at the cut end of a vertical stem, 
it at first grew horizontally for a short distance—when it 
did not come in contact with solid bodies—and then down- 
ward (Fig. 19, w,). In stems lying horizontally the root 
grew directly downward. In animals thus operated upon, 
adventitious roots were also often formed at the middle of the 
stem. I have never found these adventitious roots upon the 
uninjured animals taken from the ocean. They grew directly 
downward toward the earth (Fig. 19, w2). The phenomenon 
seemed strangest of all when such adventitious roots arose 
from a stem fixed in the sand in an inverted position (with 
the tip down); in this case the root grew toward the apical 
end of the animal. At times these downward-growing roots 
showed torsions such as are found in winding plants. 
8. The newly formed main stems behave in a way oppo- 
site to that of the roots; they grow vertically upward. This 
contrast between the root and main stem is shown most beau- 
tifully when new stems with polyps arise from the newly 
formed root itself. In Fig. 19 is shown a branch which, 
after having been deprived of its tip, was fixed vertically in 
the sand with its tip directed upward. In place of the tip 
a new root w, grew from the main stem, at first horizontally 
and then downward. A young branch s arises from the 
root w, and grows vertically upward. 
In another stem all the lateral branches had gone to 
pieces; it had been suspended vertically. I believed that 
the animal had died, when from the middle of the stem 
branches began to arise, which proved to be both roots and 
polyps; the roots sprang from the lower portions of the stem, 
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