HETEROMORPHOSIS 1338 
and, according to the experiments thus far made, the method 
by which this is accomplished consists in cutting off the tips 
and roots of the stems, and suspending the stems vertically 
in the aquarium with their bases pointing upward. 
5. When such segments from which the tips and the roots 
have been cut off are laid horizontally, and in such a way 
that they are surrounded by water on all sides, roots grow 
only from the aboral ends of the fragments, while, as a rule, 
new tips grow from the oral ends. Exceptionally, however, 
roots grow from the oral ends also. 
6. Bearing in mind the fact that roots may arise from 
either cut end and under all conditions, we may say that 
biapical animals may be produced by leaving the tips intact 
and cutting off the stems close to the root. If such stems 
are suspended vertically, with their tips downward, new tips 
may arise at the aboral end. If bibasal animals are desired, 
stems deprived of their tips are cut off close to the root, and 
are suspended vertically in the aquarium, with their tips 
downward. In all my experiments thus far performed only 
roots have been formed at the cut ends directed downward, 
while tips or roots have been formed at the cut ends directed 
upward. Besides the influence which the position of the 
stem has upon the formation of organs, another at present 
unknown, and therefore uncontrollable, factor exists which 
renders possible the growth of a root at the cut end which is 
directed upward. Yet I believe it possible that purcly 
external conditions (which were satisfied in the aquarium, 
and which possibly some day may be brought under con- 
trol) determine this strong tendency toward the formation of 
roots. 
It still remains to be investigated whether gravity or light 
or both circumstances have an influence upon the formation 
of the organs in thiscase. In all my experiments performed 
thus far in the dark room, no regeneration whatsoever of the 
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