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, lOj). 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, w 2 ). 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 u\ 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, 



