394 Hooker: Movement in Drosera rotundifolia 



They contract at each end so that they have the appearance of 

 dumb-bells, and finally separate into several disk-shaped parts. 

 In extreme cases they separate into a large number of droplets 

 which exhibit Brownian movement. No marked difference was 

 observed in the size of the rabdoids on opposite sides of the tentacle 

 in the bending region, and no alteration was visible during move- 

 ment. The function of the rabdoids is not apparent. It seems 

 probable, however, that they are connected in some way with the 

 process of secretion, rather than with the mechanics of movement. 

 Gardiner ('85) suggested that they might be reserve material or 

 some substance used up during secretion. This seems to be borne 

 out by the fact that they are of protein composition according to 

 Tunmann ('13, p. 481). 



3. Unbending by plasmolysis 



Although a two per cent, solution of potassium nitrate usually 

 plasmolyzes the cells on the convex side of a bending tentacle, this 

 does not cause the tentacle to become straight (see De Vries, '86, 

 p. 5). More concentrated solutions produce unbending. For a 

 short time after the tentacle is fully bent complete plasmolysis 

 still causes unbending, but when the tentacle has been bent a 

 considerable period and during unbending, plasmolysis does not 

 alter its shape. 



The xylene experiment which W. H. Brown ('12, '16) made on 

 Dionaea and Mimosa was tried on Drosera tentacles, but no positive 

 results were obtained. Bent and bending tentacles were killed 

 in boiling water, treated with 95 per cent, alcohol, absolute alcohol 

 and xylene. No unbending ensued. This may indicate a dif- 

 ference between the mechanics of movement in Drosera and in 

 such plants as Dionaea and Mimosa. However, the failure of the 

 experiment may have been owing to faulty technique, although 

 the description of the process by Brown ('16, p. 78) was followed 

 in detail. 



HI. DISCUSSION 

 I. Increased turgidity as the means of movement 

 The straightening of bent tentacles by plasmolysis shows the 

 cell elongation, which is the immediate cause of bending, to be a 



