go MOVEMENTS OF CURVATURE 



The aggregation and precipitation produced by stimulation gradually pass away 

 again, not only in the cells of intact tentacles, but also in sections cut from them. 

 In the latter case repeated washing accelerates the solution of the precipitated 

 materials by removing the soluble diosmosing products as fast as they are formed. 

 The precipitation resulting from stimulation can only be regarded as a chemical 

 reaction due to the production of a precipitating substance, whereas the protoplasmic 

 aggregation as well as the changes in shape and differentiation of the nucleus 

 are vital responses l . That the aggregation is associated with the secretory activity 

 is shown by the fact that it is produced by nitrogenous and other substances, not 

 only in the cells of the tentacle stalk of Drosera, but also in cells of the non-motile 

 glands of Sarracenia, Nepenthes, and Drosophyllum 2 , and can apparently be also 

 induced in many cells which have a somewhat analogous power of secretion. It is 

 also known that changes of shape are shown by the nucleus and cytoplasm of a few 

 plant-cells and various animal-cells 3 during active secretion. This is in accord with 

 the fact that many chemical agencies which act fatally when concentrated, induce 

 various changes in the shape and visible structure of the protoplasm when applied in 

 diluted form. 



The conduction of the stimuli. The visible nature of the aggregation and precipita- 

 tion enables the progress of the excitation to be followed from cell to cell. It has, 

 however, not yet been determined by comparison whether the motory and aggregation 

 reactions involve the conduction of a single or of two separate stimulatory processes. 

 Darwin 4 observed that when the head of a tentacle of Drosera was moderately 

 strongly stimulated, a neighbouring decapitated tentacle curved but showed no 

 aggregation, whereas aggregation appeared in the head of a neighbouring intact 

 tentacle, and spread in a reflected fashion downwards in the cells of the stalk. 

 Apparently, therefore, a stimulus inducing aggregation was propagated from the head 

 in the reverse direction to the primary stimulus inducing curvature and exciting 

 the head. When the stimulus is more intense, however, the aggregation is directly 

 propagated to a greater distance and spreads to neighbouring decapitated tentacles. 



If the stimuli for each reaction are distinct, they are at least conducted along the 

 same path, that is in the parenchyma cells and in the living elements of the vascular 

 bundles. That the parenchyma cells are capable of conduction is shown by an 

 experiment of Darwin's in which the vascular bundles were cut across and yet 

 a stimulus was transferred through the tentacle. In addition the aggregation may 

 be propagated from cell to cell of the epidermis. According to Batalin 5 , stimuli 

 travel more rapidly along the vascular bundles than through the parenchyma. This 

 is probably the result of the elongation of the living cells of the vascular bundles, 



1 Precipitating substances are not present in all secreting cells, even of carnivorous plants, and 

 hence, according to Goebel (1. c., p. 119, footnote), no granulation is produced in the secretory gland- 

 cells of Utricularia and Pinguicula as the result of stimulation. 



2 Cf. Schimper, 1. c., p. 231 ; Goebel, 1. c., p. 199. 



3 For the literature see Rosenberg, 1. c., p. 112. 



4 Darwin, Insectivorous Plants, p. 242. [Darwin does not state that the decapitated tentacle 

 showed no aggregation, but that it showed less aggregation, and further, the aggregation disappears 

 first at the base of the tentacle and travels upwards.] 



5 Batalin, Flora, 1877, p. 66. Cf. also Zeigler, Compt. rend., 1874, T. Lxxvm, p. 1417. 



