266 T. H. MORGAN. 



of a basal hydranth. (7?) The hydranth may produce some 

 materials that inhibit the development of other hydranths from 

 the remainder of the piece ; hence the inhibition, as long as a 

 hydranth is present or developing. On first thought these alterna- 

 tives would seem to cover the only possible ways in which the 

 problem of regeneration may be presented at least as long as 

 the problem is confined to purely physiological actions of a chemi- 

 cal order. There are, however, not a few considerations indicat- 

 ing that the fundamental interpretation may lie in a different con- 

 ception of the problem. I shall try here to emphasize this other 

 point of view without attempting to develop it into a theory of 

 regeneration. At most we may hope at the present time to find 

 in the facts some indication of the nature of the problem if not 

 its entire elucidation. 



A number of experiments have been made that seem to indi- 

 cate that the temporary inhibition of the development of the basal 

 hydranth in Titbnlaria is not the result either of the using up of 

 materials by the oral hydranth, or of the setting free of inhibi- 

 tory stuff. The simultaneous development of hydranths at both 

 ends of a piece, which frequently occurs in short pieces, is a case 

 in point. Both ends develop at the same rate as when a single 

 hydranth develops, and not half as fast as the hypothesis demands. 

 Again the development of a basal hydranth does not appear to 

 inhibit the oral development as we should expect if the result 

 were dependent simply on the presence of materials in the stem. 

 Some experiments of MacCallum's with plants have an impor- 

 tant bearing on this point. If the terminal bud of the bean is 

 removed, the buds in the axils of the cotyledons develop. But 

 if the activity of the terminal bud is simply lessened by inclosing 

 that part in an atmosphere of hydrogen, the basal buds do not 

 develop. Hence the result is due not to activity of the terminal 

 end, but to its presence or absence. In a different way the same 

 fact is brought out. A piece of willow stem is cut off, its middle 

 third is inclosed in a tube filled with moist air, so that the buds 

 in this part are encouraged to begin their development ; the dry 

 air retarding the development of those outside. After the middle 

 buds have unfolded, the entire piece is inclosed in a moist 

 chamber, when the more apical buds sprout forth, while none 



