MOVEMENTS PRODUCED BY CONTACT-STIMULATION 85 



has already been shown to be connected with a transitory acceleration of growth, 

 and the bending of the sporangiophores of Mucorineae is also a growth-curvature. 

 Batalin's * measurements, though not fully satisfactory, indicate the same to be the 

 case for Drosera. Here also a transitory acceleration of growth appears to result 

 from stimulation, but further research is required to make this certain. The con- 

 clusion that we are dealing with a growth-curvature is supported by Corren's observa- 

 tion that the curvature* remains permanent when a stimulated tentacle of Drosera 

 is suddenly killed by immersal in boiling water 2 . 



As in the case ot tendrils, the causes inducing the changed rates of growth are 

 unknown. De Vries' 3 supposition that the curvature was in the first instance due to 

 an elastic stretching of the cell-wall by turgor is as inapplicable to the tentacles 

 of Drosera as to tendrils, and in any case the curvature of the unicellular sporangio- 

 phore of Phycomyces could hardly be due to a rise of turgor unless the cell-wall on 

 the convex side became at the same time more extensible. 



SECTION 19. Curvatures produced by Chemical Stimuli. 



We are here concerned primarily with the curvatures due to diffuse 

 chemical stimuli, such as must occur whenever the growth of the opposite 

 sides of a dorsiventral organ is unequally affected. Chemonastic reactions 

 of this kind, like thermonastic responses, are rarely pronounced in character, 

 but the action of chloroform causes a strong curvature in the pulvini of 

 Mimosa pudica*, as well as in tendrils 5 , which also respond to treat- 

 ment with a dilute solution of iodine. In addition, the rarification of the 

 surrounding air causes, when pronounced, a certain alteration in the position 

 of the leaflets of Mimosa and of the stigmas of Mimulus 6 . 



This power of chemonastic movement is, however, especially well 

 developed in certain carnivorous plants, and it is shown in response to such 

 substances as proteids, salts of ammonium, and phosphates. The chemo- 

 nastic movement resembles that produced by contact-stimulation in the 

 case of the tentacles of Drosera and the leaves of Pinguicula. Contact, 

 however, causes a sudden closure of the leaflets of Dionaea^ whereas chemical 

 stimulation induces a gradual closure, which may take as long as a day 

 when the stimulus is a feeble one 7 . In addition, after mechanical stimu- 

 lation the leaves remain hollow so that they enclose a cavity, whereas 



1 Batalin, Flora, 1877, p. 39. 2 Correns, Flora, 1892, p. 126. 



3 De Vries, Bot. Ztg., 1886, p. 5. * Pfeffer, Physiol. Unters., 1873, p. 64. 



5 Correns, Bot. Ztg., 1896, p. 16. This author also states that ammoniacal vapours induce 

 a certain curvature in tendrils. 



6 Correns, Flora, 1892, pp. 97, 146, 148. On Mimosa cf. also Bonnier, Revue generate de 

 botanique, 1892, T. iv, p. 525. 



7 Darwin, Insectivorous Plants, 1875, p. 397. The progress of the movement was also followed 

 in detail by Darwin (The Power of Movement in Plants, 1880, pp. 239, 241, 261). 



