180 Contractility of the Protoplasm of Plant Cells. [Nov. 24, 



obtained in the case of Drosera (loc. cit.) : the protoplasm seeming 

 to be partially paralysed, the whole of its energy apparently expended 

 in endeavouring to protect itself from the abnormally rapid with- 

 drawal of water. The passive shrinking produced by strong dehy- 

 drating reagents is essentially different from the active contraction 

 arising from normal stimulation, and one may well inquire whether 

 the effects produced by plasmolysis at all tally with those vital 

 processes which actually take place under ordinary circumstances in 

 plant cells. 



The results obtained with Mesocarpus demonstrate that we have 

 here a plant cell wmich reacts in a most powerful manner to the 

 stimulus of temperature, of light, of electricity, and of poisons, and 

 that this reaction, which may be watched under the microscope, is 

 attended by a diminution in size. In the opinion of the author such 

 a series of reactions can only point to one property of the protoplasm, 

 viz., that of contractility, and taking into consideration the whole of 

 the observations, there appears to be no doubt that the protoplasm of 

 plant cells, like that of animal cells, is capable of active contraction. 

 The author believes that in all irritable organs the movements are 

 brought about in consequence of a definite contraction of the proto- 

 plasm of the irritable cells, and that during such contraction some of 

 the cell sap escapes to the exterior. At the same time the elastic cell 

 wall contracts pari passu with the protoplasm. The author has 

 already drawn attention to the intimate connexion between the proto- 

 plasm and the wall (' Phil. Trans.,' 1883, Part 3), and has shown that 

 even after pronounced plasmolysis, the ectoplasm of the primordial 

 utricle is always connected to the cell membrane by very numerous 

 and delicate strands of protoplasm. The protoplasm may be with- 

 drawn from the wall by a very strong electric shock, but the normal 

 effect of a moderate stimulus is to cause the protoplasm to con- 

 tract, and in certain cases pull upon its wall, while in very turgid 

 cells where the cell wall is in a state of great tension, the wall for the 

 most part simply contracts upon the protoplasm. The escape of 

 liquid from the interior of the cell is regarded as being due to filtra- 

 tion under pressure. The author is unable to uphold Pfeffer's theory 

 that the sudden abolition of turgidity is dependent upon the destruc- 

 tion of a certain quantity of an osmotically active substance. In his 

 opinion there is in every cell a sufficient quantity of osmotically 

 active substance to ensure turgidity, but the increase or decrease 

 of turgidity essentially depends on the contraction or relaxation 

 of the primordial utricle. His experiments all tend to show that 

 it is the ectoplasm which mainly determines the state of turgidity of 

 the cells. Thus in the tentacle cells of Drosera, the endoplasm may 

 actually be withdrawn from the ectoplasm by the lengthy action of 

 strong solutions of magnesium sulphate, and although it is almost 



