1885.] 



in the Tentacles of Drosera dichotoma. 



231 



before referred to, all the central core of the meshwork has for the 

 most part disappeared, and replacing it is a single large vacuole filled 

 with cell sap. The ectoplasm has moreover contracted from the upper 

 or free surface of the cell-wall. In no case does this destruction 

 and consequent vacuolation extend to the base of the gland-cells 

 where the nucleus is situated. The nucleus is always surrounded 

 by dense protoplasm ; and there are grounds for believing that 

 after very long stimulation, when all the secretion has been poured 

 out, and before absorption begins, an active growth of protoplasm 

 takes place around the nucleus and in the more basal portion 

 of the cell. In certain cases the secretion can be seen under the 

 microscope to escape in drops — apparently through the pitted 

 portions of the cell- wall — and the drops rapidly taking up water 

 and being forced outwards, assume a rod-like form, and present a 

 halo-like appearance around the gland. This 1 also occurs in the 

 mucilage-secreting cells of the bladders of Utricularia. The exact 

 part taken by the layer of cells beneath the gland-cells has yet to 

 be determined. After stimulation their vacuoles are occupied by 

 large drops of cell sap, which is of a purple or even black colour. 



The view here taken (which is supported by certain of the staining 

 reactions) with regard to secretion is, that in the gland-cells the 

 mere peripheral network consists of protoplasm, together with some 

 formed substance derived from it, and that the outpouring of the 

 secretion is caused by the repeated breaking down (owing to stimula- 

 tion) of the protoplasm into this formed substance, which is of a 

 mucous nature, and which rapidly attracts water and so escapes, as 

 the secretion to the external surface. 



Changes in the Sialh Cells. — The chief phenomena induced in the 

 stalk cells either by contact by electrical stimulus or by feeding are, 

 that the protoplasmic utricle swells up and encroaches on its own 

 vacuole, that granules rapidly appear in the protoplasm, and that the 

 movements of rotation increase in vigour. Also the cell becomes less 

 turgid, and after long stimulation the plastoid and the nucleus both 

 tend to become spherical. These changes are most markedly exhi- 

 bited in tentacles stimulated with food. The protoplasm in swelling 

 up abstracts water from its own vacuole, and in so doing leaves the 

 tannin in the sap, in a comparatively concentrated condition. The 

 outlines of the protoplasmic utricle are now rendered clearer than 

 before. As previously stated, the movements of rotation become 

 quickened very considerably, and numerous waves with high crests 

 appear on the surface of the protoplasmic utricle, and are well 

 registered by the corresponding disturbances in the cell sap. The 

 phenomenon of the protoplasmic waves breaking over the nucleus with 

 crests reaching nearly across the vacuole is very remarkable. The 

 long and narrow shape of the cells, and the combined swelling of the 



