566 LECTURE XXI. 



whether or not there exists any relation between these 

 changes in the protoplasm of the stalk-cells and the move- 

 ment of the tentacle, that is, whether or not the occurrence 

 of aggregation in the stalk-cells is an essential condition 

 of the inflexion of the tentacle. Darwin, it is true, states 

 definitely that aggregation may take place without inflexion ; 

 but naturally no movement can take place, except a shorten- 

 ing like that of the filaments of the Cynareae, if all the 

 cells of the tentacle undergo aggregation simultaneously. 

 He does not, however, express himself definitely as to the 

 possibility of inflexion without aggregation, though he inci- 

 dentally mentions, when speaking of the action of acids on 

 the tentacles, that they caused the tentacles to bend without 

 causing true aggregation. Much importance cannot be at- 

 tached to this observation, inasmuch as most of the acids 

 used proved to be highly poisonous to the plant. From 

 Gardiner's observations it appears that the inflexion of the 

 tentacle on stimulation is due to the occurrence of aggre- 

 gation in the cells of the concave side, that is, to the abolition 

 of their turgidity. 



Without going so far as to assert that a process of ag- 

 gregation, identical with that induced in the cells of the 

 tentacles of Drosera, takes place in the cells of every motile 

 organ when it is stimulated, we may reasonably infer that 

 the protoplasm in the cells of these organs undergoes some 

 molecular change, and in view of the mechanism of the move- 

 ments, it seems probable that the effect of this molecular 

 change is to diminish the resistance which the protoplasm 

 offers to the escape of the cell-sap by filtration under pres- 

 sure. It is a further question, and one which it is at present 

 impossible to decide, whether or not the protoplasm, whilst 

 thus becoming permeable, actually contracts upon its con- 

 tents, like the wall of a contractile vacuole. It is not neces- 

 sary, for the purpose of explaining the sudden loss of tur- 

 gidity in the stimulated cells, to assume that the water is 

 forced out by an active contraction of the primordial utricle, 

 for the pressure of the stretched elastic cell-wall is sufficient 

 for the purpose. But it is worth while to bear in mind that 



