366 
Notes. 
processes which actually take place under ordinary circumstances in 
plant-cells. 
The results obtained with Mesocarpus demonstrate that we have 
here a plant-cell which 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 my opinion such a series of re- 
actions can only point to one property of the protoplasm, viz. that of 
contractility, and taking into consideration the whole of the observa- 
tions, there appears to be no doubt that the protoplasm of plant-cells, 
like that of animal cells, is capable of active contraction. I believe 
that in all irritable organs the movements are brought about in con- 
sequence of a definite contraction of the protoplasm 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. I have already drawn attention to the in- 
timate connection between the protoplasm and the wall (Phil. Trans. 
1883, Part 3), and have 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protoplasm may be withdrawn from the wall by a very strong electric 
shock, but the normal effect of a moderate stimulus is to cause the 
protoplasm to contract, and in certain cases pull upon its wall, while in 
very turgid cells, where the cell-w'all 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 filtration under pressure. I am unable to uphold Pfeifer’s theory 
that the sudden abolition of turgidity is dependent upon the destruc- 
tion of a certain quantity of an osmotically active substance. In my 
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. My 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 partially be 
withdrawn from the ectoplasm by the lengthy action of strong solutions 
of magnesium sulphate, and although it is almost entirely collected 
around the nucleus at the centre of the cell, the latter still remains 
turgid. 
