146 
Sydney H. Vines. 
Ihese induced movements consists essentially in a change in the turgidity 
of the parenchymatous cells of the motile organ. Brücke 1 ) proved that 
the down ward movement of the leaf of Mimosa pudica, which follows a 
Stimulus, is due to a diminution of the tension in the lower porlion of 
the motile organ. The experiments of Pfeffer 2 ) upon the stamens of 
Cynareae and upon the motile organs of Mimosa pudica demonstrated, 
that a considerable quantity of water is expelled from the tissues during 
the movement. Pfeffer suggested that, assuming the permeability of the 
teuse cell-wall to remain unaltered, the expulsion of cell-sap from the 
cell maj be dependenl upon changes in the protoplasm. Under ordinary 
circumslances, as has been already mentioned, the protoplasm does not 
permit the escape of cell-sap, but it may be that some inlluence so acts 
upon the protoplasm al the time of movement, that it becomes permeable. 
In commenting upon this Suggestion Sachs 3 ) remarks, that such variations 
in the permeability of protoplasm are known to occur. For inslance, 
when the protoplasm of a cell of Spirogyra contracts previously to con- 
jugation, it must have become permeable, for a quantity of cell-sap escapes. 
The force which causes the expulsion ol the cell-sap, is regarded by 
Pfeffer 4 ) as being merely the pressure of the elastic cell—wall upon the 
cell-conlents, to which the now permeable protoplasm olTers but little 
resistance. He believes that the cause of the Variation of pressure is to 
be sought in some change effected in the osmotic properties of the cell- 
conlents by the action of the Stimulus. It is by no rneans easy to 
understand, how such a diminution of the osmotic properties of the 
cell-contents could be so rapidly produced. It seems more simple and 
satisfactory to regard the expulsion of the cell-sap as being due to a 
contraction of the protoplasm, that is, to an approximation of its micellae 
in consequence, probably, of an increase of the atlraction existing between 
them, ellected either by a Stimulus acting from within (spontaneous 
movements) or by a Stimulus acting from wilhout. The escape of the 
fluid under these circumslances is to be regarded as a phenomenon not 
of osmosis, but of filtration under pressure. 
The position which spontaneously motile organs assume when ex- 
posed to light is that in which they are fully expanded. Proceeding 
upon the assumption that the mechanism of the movements of these or¬ 
gans is essentially the same as that of the induced movements of irri¬ 
table organs, this expanded position must be ascribed to the maintenance 
of the micellae in a condition of stable equilibrium. The intluence of 
light upon the micellae is of such a nature that it prevents their approxi- 
1 ) Areb. f. Anat. u. Physiol. 1848. 
i) Physiol. Untersuch. 1873. 
3) Lehrbuch p. 866. 
4) Osmot. Untersuch, p. 192- 
