CURVATURES PRODUCED BY CHEMICAL STIMULI 89 



along the stalk of the tentacle \ These intracellular aggregations involve in the cells 

 of the tentacle-stalk, according to de Vries, Gardiner, and Schimper, an increase 

 in volume of the protoplasm and a decrease in volume of the cell-sap 2 . At the 

 same time active protoplasmic streaming is excited, and the vacuoles increase 

 in number. The shapes of the vacuoles also alter, and this naturally involves 

 changes of shape in the protoplasm, although Darwin attached undue importance to 

 the latter. A little later a precipitate, the granulation 8 , usually appears in the 

 cell-sap when strong chemical stimuli are applied, but it is usually absent after weak 

 mechanical or chemical excitation. The precipitate is usually due to the excretion 

 of tannin into the cell-sap, which finally forms rounded masses, often tinged red 

 owing to the absorption and accumulation by them of the red colouring-matter 

 in the cell-sap 4 . It need not, however, always be tannin which separates out and is 

 precipitated, although similar precipitations are produced by the action of ammonium 

 carbonate, caffein, and other substances in the cell-sap of many other plants which 

 contain tannin. 



Hence it is possible that the granulation resulting from stimulation is also due 

 to the production of substances which precipitate the tannin in the same way that 

 ammonium carbonate does when applied to the head of a tentacle. Since mechanical 

 stimulation may influence the secretory activity, it may also lead when sufficiently 

 intense to a sufficient production of the materials responsible for the precipitation. 



The intracellular changes have not been followed any further in the living gland- 

 cells at the head of the tentacle of Drosera. According to the researches of Huie, 

 and also of Rosenberg, carried out on fixed material, these cells show a decrease 

 in the volume of the protoplasm and an increase in the volume of the cell-sap after 

 stimulation, that is exactly the reverse changes to those occurring in the cells of the 

 stalk. It remains to be seen, however, whether the difference is due to the fact that 

 the observations on the heads of the tentacles were made on fixed material, but those 

 on the stalk-cells upon living material. It is possible that the active excretion of 

 mucilage and other materials from the gland-cells may lead to a diminution in their 

 protoplasmic contents 5 , and in fact the amount of chromatin in the nuclei of the 

 gland-cells of animals appears to decrease greatly in amount during active secretion. 

 Both Huie and Rosenberg have found that, especially after long chemical excitation, 

 the nuclei of the gland- and stalk-cells decrease in volume, while their chromatin 

 threads assume an appearance and differentiation resembling the initial stages in 

 mitolic nuclear division. 



1 Gardiner, 1. c. 



2 On the changes of volume in the cell cf. Pfeffer, Plasmahaut u. Vacuolen, 1890, p. 290. 

 According to de Vries (1. c., p. 30) the turgor of the cell as determined by plasmolysis is uninfluenced 

 by the aggregation, whereas Gardiner (1. c., p. 232) assumes on insufficient grounds that a fall of 

 turgor ensues. 



3 The term was suggested by Goebel, Pflanzenbiol. Schilderungen, 1893, Bd. II, p. 198. Darwin 

 (1. c., p. 263) found that aggregation is produced in the leaf of Dionaea by chemical but not by 

 mechanical excitation. 



4 Pfeffer, Unters. a. d. bot. Inst. zu Tubingen, 1886, Bd. II, p. 244 ; Flora, 1889, p. 52. 



5 It is uncertain what the importance of Gardiner's ' rhabdoid ' may be (1. c., p. 230). This 

 structure occurs in the cells of Drosera and Dionaea and, according to Gardiner, increases in size as 

 the result of stimulation, whereas Macfarlane (1. c., p. 36) could detect no such increase of size in the 

 rhabdoid of Dionaea. 



