Hooker: Movement in Drosera rotundifolia 401 



ditions, of pressure-distribution, tissue-tension, etc., which are 

 estabUshed in the cells on opposite sides of the originally straight 

 organ as a result of an attempted or executed reaction." 



The inequality of conditions that should constitute the auto- 

 tropic stimulus may be found in the changes produced by the dif- 

 ference of osmotic concentration observed in bending roots and 

 tentacles, since just such a difference induces an analogous reaction 

 in hydrotropically stimulated roots. It has been emphasized 

 elsewhere (Hooker, 'i6, p. 21) that the increase in the rate of 

 growth which produces the unbending of Drosera tentacles pro- 

 ceeds in the same manner as that which causes bending, in both 

 cases commencing near the base and extending apically. More- 

 over, the amount of growth that occurs during unbending is nearly 

 the same in amount and is distributed in much the same manner 

 as during bending, so that the unbent tentacle is straight and 

 reaches approximately the same position it held before the re- 

 action. This nice regulation is intelligible when we consider that 

 the changes resulting from the decrease in osmotic concentration 

 during bending are directly proportional to the increase in volume 

 of the growing cells. It is not to be denied that other factors may 

 cooperate in producing the autotropic reaction, but the striking 

 similarity with hydrotropic reactions indicates that the effects of 

 the difference in osmotic concentration during bending are most 

 significant. 



When an insect is caught and digested, the unbending of the 

 tentacle is postponed a considerable time, occasionally several 

 days. It would appear that the absorption of food material 

 through the gland inhibits the reaction to the inequality of con- 

 ditions produced by the bending. All the cells of the tentacle 

 from base to apex are generally aggregated while food is being 

 absorbed. According to Gardiner ('85) the state of aggregation 

 is accompanied by a loss of water and he found that the injection 

 of water into the tissue stopped aggregation at once and restored 

 the cells to their normal condition. This probably accounts for 

 the fact that the osmotic concentration in the cells of bent tentacles 

 is higher than under any other circumstances. When absorption 

 ceases, aggregation stops and the tentacles unbend in the normal 

 manner. This is brought about by increased turgidity of the cells 



