196 STUDIES IN GENERAL PHYSIOLOGY 



the upper surface of the lowest element. That stems are 

 formed upon the upper, while roots are formed upon the 

 lower, surfaces of the stem, when it occupies any other 

 than a vertical position, is best shown when stems of an 

 Antennularian are suspended horizontally in the aquarium 



so as to be surrounded on all 

 sides by water. If the experi- 

 ment is continued for a long 

 time, other phenomena occur, 

 especially root formations, a 

 discussion of which we shall 

 give later. If this fact is borne 

 in mind, Fig. 40 may serve to 

 illustrate such an instance. In 

 Fig. 41 is shown how a new 

 stem arises from the basal cut 

 end and from the upper surface 

 of a stem lying horizontally. 



II. CONTINUATION OF THESE 

 EXPERIMENTS AND HETERO- 

 MORPHOSIS IN UNINJURED 

 ORGANS 



1. It is not only possible 

 by the aid of gravity to cause 

 the growth of another organ 

 in place of one that has been 

 lost, but we can also cause an 



FIG. 46 



uninjured organ to grow into 



a typical organ of a different kind by making use of the 

 same force. 



If a piece is cut from the stem of an Antennularian, and 

 this is laid horizontally into the aquarium so as to be sur- 

 rounded by water, the tiny lateral branches situated on the 

 under side of the stem begin to grow after some time 



