152 MOVEMENTS OF CURVATURE 



any movements performed can only be due to the imbibition and swelling 

 of the cell-walls. This applies to the hygroscopic movements of many 

 dry fruits as well as of the awns of Grasses and of Eroditim^ although 

 when the parts are still turgid the cohesion-mechanism may produce the 

 first movements. It is possible that both mechanisms may produce the 

 same kind of movement, so that Steinbrinck and Schwendener 1 may each 

 be partly right, although the former ascribes the opening and closing of the 

 anthers to the water-cohesion-mechanism, and the latter to imbibition 

 and swelling. 



The movement naturally in all cases depends upon the properties of 

 the organ, upon the power of swelling of the walls, and upon their rigidity and 

 the arrangement of the cells and tissues 2 . The power of imbibition varies 

 in the different layers of the cell-wall, so that the swelling may not be 

 equal in all directions. Since imbibition takes place with great energy, 

 movements due to the swelling of the cell-walls can overcome more resistance 

 than those due to the water-cohesion-mechanism, which is usually unable to 

 produce any distinct changes of shape in thick-walled cells. Both the 

 cohesion- mechanism and the decreased swelling of the cell-walls may 

 be responsible for the dehiscence of different fruits, and may produce in 

 many cases strains which when released cause sudden movement. In the 

 annulus of the sporangia of Polypodiaceae, as the water evaporates from 

 the cells they are more and more contracted and deformed, the thin 

 outer walls being drawn inwards. When the strain reaches a certain limit 

 the walls of the sporangium rupture at the loosened lip-cells. Immersal in 

 glycerine excites dehiscence by removing the water rapidly from the 

 annulus-cells, and after the water in the annulus-cells has ruptured the 

 recurved annulus straightens more or less. 



Historical. The existence of movements due to death, or to changes in the 

 moistness of dead organs, was recognized by de Candolle 3 , and these were distinguished 

 from movements due to vital activity by Dutrochet 4 , who also gave explanations of 

 the movements of dehiscence and dispersal which were in the main correct. 



The influence of the external conditions can be predicted in the case of dead 

 objects from purely physical considerations, although the external conditions may 

 also affect the course of the preparation for dehiscence and dispersal. Changes in 

 the percentage of water may, for instance, act both physiologically and physically, 



1 Schwendener, Sitzungsb. d. Berl. Akad., 1899, p. 101 ; Steinbrinck, Ber. d. bot. Ges., 1901, 

 p. 552; 1902, p. 117; 1903, p. 217; Schrodt, Ber. d. bot. Ges., 1901, p. 483; Schwendener, 

 Sitzungsb. d. Berl. Akad., 1902, p. 1056; Ursprung, Jahrb. f. wiss. Bot., 1903, Bd. xxxvin, p. 635. 



2 Cf. Haberlandt, Physiol. Pflanzenanat., 2. Aufl., 1896, p. 465, and the works quoted by 

 Haberlandt on p. 488. 



3 A. P. de Candolle, Physiologic des Plantes, a German translation by Roper, 1833, Bd. I, p. 13. 



4 Dutrochet, Memoires pour servir a 1'histoire d. vegetaux et d. animaux, Bruxelles, 1837, 

 PP- 225, 235. 



