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. Imf 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 
uninjured organ to grow into 
atypical 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 — 
FIG. 46 
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