HETEROMORPHOSIS 133 



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 purely 

 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 this case. In all my experiments performed 

 thus far in the dark room, no regeneration whatsoever of the 



