I From the Bulletin of the Torrey Botanical Club, 44: 389-403. 10 Au 191 7 J 



Mechanics of movement in Drosera rotundifolia* 



Henry D. Hooker, Jr. 



CONTEXTS 



I. INTRODUCTION 389 



II. EXPERIMENTAL DATA 389 



1. Osmotic coxcentratiox 389 



2. Rabdoids 393 



3. Unbending by plasmolysis 394 



III. DISCUSSION 394 



1. Increased turgidity as the means of movement 394 



(a) Osmotic concentration 395 



(6) Permeability 397 



(c) Cell-wall elasticity 397 



2. Comparison with geotropic movements 398 



3. Alteration of cell-wall elasticity 399 



4. Autotropic nature of unbending 400 



(a) Comparison of autotropic with hydrotropic stimulus 400 



(&) Internal changes that follow bending 400 



IV. SUMMARY 402 



I. INTRODUCTION 



Plant growth is defined technically as any permanent change 

 of shape or size produced by the activity of the plant {cf. Jost, '13, 

 p. 339; Pfeffer, '06, p. i). The movements of Drosera tentacles, 

 being reactions to stimuli, are determined by the activity of the 

 Drosera plant. Moreover, bending is accompanied by a perma- 

 nent elongation of the convex side of the tentacle and unbending 

 by a corresponding increase in the length of the concave side 

 (Hooker '16). These movements are therefore phenomena of 

 growth. The term "growth" obviously includes a number of 

 processes, which may be determined by changes in the amount of 

 protoplasm, cell-wall material or osmotically active substances. 



II. EXPERIMENTAL DATA 



I . Osmotic concentration 

 In order to obtain a more detailed knowledge of the growth 

 which brings about the movement of Drose ra tentacles, the con- 

 * Contribution from the Osborn Botanical Laboratory. 



. 389 



