"POLARITY" CONSIDERED AS A PHENOMENON OF 

 GRADATION OF MATERIALS. 



BY 



T. H. MORGAN. 



In my paper^ entitled "An Attempt to Analyze the Phenomena 

 of 'Polarity' in Tubularia" I offered an interpretation of certain 

 experiments carried out by Stevens and myself.^ In another 

 paper,^ "An Analysis of the Phenomena of Organic Polarity," 

 written at about this time the same interpretation was applied 

 to the general question of polarity. These attempts to analyze 

 the problem suggested a number of new experiments in which 

 the conclusions could be tested further, and I shall give in the 

 following pages the results of some new work on Tubularia. 



I may recall my hypotheses that the phenomenon of polarity in 

 Tubularia depends on the graded distribution of materials from 

 the hydranth to the stolon. This gradation is the basis in which the 

 formative action takes place and produces the new hydranth. 

 The stimulus calling forth the reaction is the presence of a free 

 end.* From the previous experiments and from those to be 

 described here the following conclusions may be drawn: 



(1) That a gradation of hydvanth-forming substances is present 

 in the stem of Tubularia^ and that the amount present at any level 

 determines the rate at which both the oral and the basal hydranth 

 develop. 



(2) That in addition to the quantitative factor the direction of 

 the gradation or the polarity is a qualitative factor in the result. 



"^Joum. Exp. Z06I., i, 1905. 



^Journ. Exp. Z06I., i, 1905. 



^Science, xx, Dec, 1904. 



^Following Driesch I have sometimes stated that the stimulus comes from the action of the sea 

 water on the free end, but it is difficult to distinguish between the action of the sea water and the 

 simple exposure of the free end (an internal factor). Since the normal regeneration of Tubularia 

 takes place in sea water we can not distinguish between these two possibilities. If regeneration could 

 be made to take place in moist air the sea water, as a factor, would be eliminated. 



