398 Hooker: Movement in Drosera rotundifolia 



cell-walls do not always return to their original condition, but are 

 frequently crumpled or wrinkled. The rate of change in the cell- 

 wall properties undoubtedly increases during the inflexion. In 

 the same way the decrease in osmotic concentration which results 

 from the increase in volume of the elongating cells is soon compen- 

 sated for by the formation of new osmotically active material, as 

 is shown by the equality of osmotic concentration on opposite 

 sides of the tentacle a short time after it has become fully bent. 

 This process too is probably initiated soon after inflexion begins, 

 with the result that no marked difference in osmotic concentration 

 is noticeable on opposite sides of tentacles which bend slowly. In 

 the last analysis, therefore, the growth which causes the inflexion 

 of Drosera tentacles is the activity of the protoplasm in manu- 

 facturing cell-wall substance and osmotically active material. 



2. Comparison with geotropic movements 



The movement of Drosera tentacles is seen to be brought about 



by the same mechanism found in geotropically reacting organs, 



where Kraus ('82, p. 87) and Noll ('88, p. 511) observed a decrease 



in the osmotic concentration of the cells on the convex side of 



roots and stems, which was particularly evident in case of rapid 



bending. The subject is well summed up by Jost ('13, p. 580) in 



the following paragraph, and his remarks apply to the bending of 



Drosera tentacles with equal felicity : 



In all cases that have been more carefully studied, the immediate cause of the 

 bending is a difference of growth in length on opposite sides. The surface growth of 

 the membranes here as elsewhere is preceded by stretching due to turgidity, and this 

 is gradually made permanent by growth. If an organ be plasmolyzed at the be- 

 ginning of the geotropic bending it again becomes straight, but later the curvature 

 is permanent. The stretching is unequal in amount on the two opposite sides. This 

 difference might consist in an increased osmotic pressure on the convex side and 

 diminished osmotic pressure on the concave side, but this is by no means the case; 

 the pressure on the concave side seems rather to remain unchanged, while that on 

 the convex side diminishes during bending. This result is not so astonishing when 

 we consider that the rate of growth does not depend directly on the amount of osmotic 

 pressure, but that this latter frequently depends on the increase in cell-volume. 

 The unequal stretching of the opposite sides due to turgidity must therefore be 

 connected with an alteration in the elasticity of the cell-walls, the convex side be- 

 coming more extensible. Of course in unicellular organs (in sporangiophores of the 

 Mucorineae, for example), the bending must depend solely on a change in the elas- 

 ticity of the cell-wall. 



