402 Hooker: Movement in Drosera rotundifolia 



on the concave side. Without doubt the same factors found to 

 determine bending are involved in the unbending, but the process 

 is so slow that it resembles ordinary plant growth. It does not 

 seem probable that this deferred reaction can be a direct response 

 to changes produced by a difference of osmotic concentration which 

 existed during bending, but is now completely effaced. In these 

 cases unbending is probably a response to changes taking place 

 as the result of a cessation of absorption and the end of the aggre- 

 gated condition. Nevertheless the effects of the difference in 

 osmotic concentration are conditioning factors of the unbending 

 reaction, for an accelerated rate of growth on the adaxial side of 

 the tentacle occurs only after previous bending. 



IV. SUMMARY 



The osmotic concentration in cells of Drosera rotundifolia ten- 

 tacles was measured by plasmolysis in potassium nitrate and 

 glucose solutions. Measurements were made on straight, bending, 

 bent and unbending tentacles. The osmotic concentration in the 

 cells on the abaxial side of the stalk, in the growing region, was 

 found to diminish during bending; no change was observed on the 

 adaxial side. The decrease in osmotic concentration is accounted 

 for by the increase in volume of the cells, and is therefore considered 

 an effect and not a cause of their elongation. There is no indica- 

 tion that changes in permeability occur. 



The elongation is produced by a decrease in the elasticity of the 

 cell-walls, and is later fixed by growth. The movement of ten- 

 tacles is therefore brought about by the same mechanism found in 

 geotropically reacting organs, where a decrease has been observed 

 in the osmotic concentration in the cells whose growth causes 

 bending. 



Similarities between hydrotropic reactions and autotropic 

 unbending of tentacles and of geotropically bent roots indicate 

 that the growth on the concave side which brings about the un- 

 bending is a response to changes resulting from the difference in 

 osmotic concentration present during bending. As in hydrotropic 

 reactions, growth takes place on the side with the higher osmotic 

 concentration. 



