Page:Insectivorous Plants, Darwin, 1899.djvu/55

 slow, and resemble those of Amoebse or of the white corpuscles of the blood. We may therefore conclude that they consist of protoplasm. [This conclusion has been shown to be erroneous: there can be no doubt that the aggregated masses are concentrations or precipitations of the cell-sap, and that their supposed amoeboid movements are the result of the streaming protoplasm, which monids the passive masses into a variety of forms.

Pfeffer was the first to insist on this view of the nature of aggregation. In his 'Osmotische Untersuchunpen' (1877). Since then the subject has been investigated by Schimper ('Botanische Zeitung.' 1882. p. 233), who describes the aggregated masses as concentrations of cell-sap, rich in tannin, and floating in the swollen and transparent protoplasm.

Schimper's observations are confirmed by Gardiner ('Proc. Royal Soc.,' Nov. 19. 1885,' No. 240. 1886), who describes the protoplasm in the stalk-cells of Drosera dichotoma as swelling up by the absorption of the "water from Its own vacuole," and thus leaving the tannin in cell-sap in a concentrated condition. Gardiner has added some curious observations on the connection between aggregation and the condition of the cell as regards turgidity. He supposes that aggregation is connected with a loss of water, and that an aggregated cell is in a condition of diminished turgidity. This is supported by his observation that "injection of water into the tissue will at once stop aggregation, and restore the cell to its normal condition." These changes are connected with certain alterations of form occurring in the above-mentioned body described by Gardiner under the name of rhabdoid, and which seems to be peculiarly sensitive to changes in the turgidity, so much so indeed that the author utilises it as a "turgometer," or index of the degree of turgescence.

H. de Vries has also written on the subject of aggregation ('Botanische Zeitung,' 1880, p. 1), and his views agree with those of Pfeffer, Schimper, and Gardiner as to the main fact that the aggregated masses are concentrations of cell-sap. In some other respects they differ from the conclusions of these authors.

De Vries believes that in Drosera and in vegetable cells generally the vacuoles are surrounded by a special protoplasmie wall, distinct from the layer of flowing protoplasm If their shapes are sketched at intervals of

. (Drosera rotundifolia.) Diagram of the same cell of a tentacle, showing the varions forms successively assumed by the aggregated masses of protoplasm.

a few minutes, they are invariably seen to have undergone great changes of form; and the same cell has been observed for several hours. Eight rude, though accurate sketches of the same cell, made at intervals of between 2 m. or 3 m..