88 MOVEMENTS OF CURVATURE 



secretory activity of the digestive glands. The secretory activity of the 

 leaf of Dionaea is in fact only aroused by stimulation, whereas the glandular 

 heads of the tentacles of Drosera continually excrete mucilage and water, 

 but do so more rapidly when chemically and also when mechanically 

 stimulated. At the same time the excretion of acid begins, so that the 

 reaction of the digestive fluid alters much as it does in the stomach of 

 a carnivorous animal 1 . Although the pitchers of Nepenthes and the leaves 

 of Drosophyllum lusitanictim have no power of independent movement, the 

 secretion of water, mucilage, and enzymes by the glands is awakened or 

 accelerated to a certain extent by chemical stimuli. Chemical excitation, 

 on the other hand, induces both movement and secretion in the case of the 

 leaf of Dionaea^ whereas mechanical excitation induces movement only 2 . 

 It will without doubt ultimately be found possible to excite excretion 

 without movement even in those cases where both occur together normally ; 

 and in fact, according to Darwin, a mechanical stimulus induces movement 

 without secretion in the leaf of Pinguictila, whereas ammonium carbonate 

 produces secretion without movement. In certain cases, however, a separa- 

 tion of this kind may not be possible owing to the fact that the excitation 

 of the motor-mechanism may unavoidably awaken changes leading to 

 secretory activity and vice versa. 



Various visible changes in the cell-contents are associated with the 

 secretory activity, and these are also shown by the gland-cells of the 

 pitchers of Nepenthes and the leaves of Drosophyllum^ which possess no 

 power of movement. These changes are therefore presumably of secretory 

 origin, although it is possible that other visible changes in the cells may be 

 associated with the response to stimulation by movement. Neither the 

 causes nor the genetic relationship of these changes are, however, satisfac- 

 torily known, although it appears as though the waxing and waning of the 

 amount of nuclear chromatin is the direct result of secretory rest and 

 secretory activity respectively. 



The intracellular changes have been studied by Darwin on Drosera rotundifolia 

 and by Gardiner also on Drosera dichotoma (= Drosera linatd)*) in which a change 

 of coloration accompanies the aggregation beginning in the head and progressing 



1 Darwin, Insectivorous Plants, 1875, p. 85. Facts in regard to other plants are also given by 

 Darwin. 



8 According to Macfarlane (Contrib. from the Bot. Lab. of Pennsylvania, 1892, Vol. I, p. 37), 

 a certain secretory activity is awakened in the leaf of Dionaea by strong mechanical or electrical 

 excitation. 



3 These changes were first observed by Darwin (1. c., p. 38), who did not, however, distinguish 

 between aggregation and precipitation (granulation), as did Schimper (Bot. Ztg., 1882, p. 231); 

 de Vries (ibid., 1886, p. i) ; and, at a later date, Gardiner (Proc. of the Royal Soc. 1886, Vol. xxxix, 

 p. 229). Huie, Quarterly Journal of Microscopical Science, 1896, Vol. xxxix, p. 387 ; 1899, Vol. 

 XLII, p. 203 ; Rosenberg, Physiol.-Cytol. Unters. iiber Drosera rotundifolia^ 1899; and Haberlandt, 

 Sinnesorgane, 1901, p. 94, have paid especial attention to the changes in the gland-cells. 



