ORGANIZATION AND GROWTH 199 
orientation of Antennularia toward the center of the earth 
are not exhausted by what has been said in the foregoing. 
It is possible to cause the growing tip of the stem to cease 
its growth and develop into a root. This is done by invert- 
ing the tip. I cut long pieces from the stems of Antennu- 
larie and hung them vertically 
in the aquarium, but in an Ww 
inverted position. <A rapidly = 
growing stem was formed at 
the upper—that is to say, the 
basal—end. When it had 
attained a certain height, I A 
turned the whole animal about 
a horizontal axis through an 
angle of 180°. Not in a single 
instance did the tips of the 
stems bend upward—as the 
negatively geotropic parts of 
plants usually do under the 
same conditions—but they 
ceased to grow and one or more 
roots formed at their tips. 
Fig. 49 shows a stem at the 
end of such an experiment; 
ab is the piece of stem upon f 
which the experiment was 
started. It was at first fixed 
in an inverted position, so that the basal end b was directed 
upward, and the apical end downward. The new stem be 
sprang from the basal extremity, grew vertically upward, 
and gave rise to lateral branches which were directed slightly 
upward and carried polyps upon their upper surfaces. The 
roots W, formed at b, at the base of the new stem, as was usually 
the case when the old stem did not stand entirely vertical. 
FIG. 49 
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