414 



Harry Ben I Torrey. 



its proximal end and parallel with the first (Fig. 4). Instead of 

 moving in the same direction, however, they move away from 

 each other as indicated by the arrows, A in the direction of less, 

 B o^ greater, resistance. 



It is clear that the factor of external resistance does not govern 

 such behavior, nor does the mechanical factor of tension, as has 

 been shown above. It is equally difficult to explain the geo- 

 tropic reactions of Corymorpha on obviously mechanical grounds 

 by means of the third hypothesis; for the response of a given cell 

 may be different, according as the stem is hung by its proximal 

 or distal end, though the contents of the cell be distributed by 



Fig. 4. 

 Diagram to illustrate geotropism. 



gravity in the same way in the two cases. This hostility to the 

 familiar mechanical explanations which appear to account for 

 the facts in other geotropic organisms urges upon me the desir- 

 ability of repeating and extending my experiments as soon as oppor- 

 tunity is afforded. It is certain, however, that the stem as a whole 

 orients itself negatively to gravity, without regard to' the point at 

 which it is supported. And the reactions of the axial cells are 

 unquestionably associated with the polarity of the stem. A 

 change in the polarity of a region of the latter is always accom- 

 panied by a change in the reactions of the axial cells in this region. 



