82 MOVEMENTS OF CURVATURE 



whereas the stamens of Opuntia and Cereus, and to a less degree those of Sparmanma, 

 and certain members of the Tiliaceae and Portulaceae, always bend towards the side 

 stimulated. 



Irritable stigmas, which close together when touched, are possessed by Alimulus, 

 Martynia, Bignonia, and Goldfussia ] . In addition the style of Glossostigma elatinoides"* , 

 and also of Arctotis 3 , curves in response to contact. 



Except in the case of Herberts, it is not known in the case of a single one of 

 these irritable stamens, stigmas, and styles whether the movement is produced by 

 growth or by elastic contraction, and the same applies to the movement of the irritable 

 labellums of certain orchids*. Hence it is impossible to say whether the cell- 

 mechanism is the same as in the pulvini of Mimosa and the stamens of Cynareae. 

 The rapid movements of Stylidium and of other objects are, however, due to the 

 sudden release of a mechanical resistance to an attempted growth-curvature 5 . 



SECTION 18. Movements produced by Contact-stimulation. 



No contact-irritability can be detected in ordinary growing stems and 

 leaves, and, according to Newcombe 6 , the same applies to the radicles of 

 seedlings, for the feeble curvatures which Sachs 7 observed as the result of 

 rubbing the growing zone strongly were traumotropic in character. Since, 

 however, the roots of Vanilla, and of a few other plants, possess distinct 

 thigmotropic irritability, it is possible that other roots may be found to be 

 more or less irritable to contact. 



Strong contact-irritability is shown by the sporangiophore of Phy- 

 comyces nitens, for when the tip is rubbed on one side a curvature of the 

 growing zone begins in a few minutes 8 . Since no reaction is produced by 

 contact below the growing zone, either the power of perception is restricted 



1 For additional instances see Hansgirg, I.e., 1893 and 1896. Cf. also W. Oliver, Ber. d. bot. 

 Ges., 1887, p. 112; Miyoshi, Journal of the College of Science, Japan, 1891, Vol. IV, p. 205; 

 Haberlandt, 1. c., 1901, pp. 55, 58. According to Burk (Bot. Centralbl., 1902, Bd. LXXXIX, p. 645) 

 the stigmas of Mimuhis and of Torenia close when pollinated owing to the withdrawal of water 

 by the swelling pollen-grains. 



a Quoted by Hansgirg, I.e., 1893, p. 149. 



3 Minden, Flora, 1901, p. 238; Haberlandt, I.e., 1901, p. 60. 



* For additional literature see Oliver and Hansgirg, 1. c., 1893, p. 150. 



5 Many such instances are given by Hansgirg, 1. c., 1893, p. 149. 



6 Newcombe, Beihefte zum bot. Centralbl., 1902, Bd. XII, p. 242. 



7 Sachs, Arb. d. bot. Inst. in Wiirzburg, 1873, Bd. I, p. 437 ; Darwin, The Power of Movement 

 in Plants. Darwin (1. c., pp. 109-71) erroneously ascribed a power of contact-irritability to the root- 

 tip, which enabled the root to curve away from solid bodies, whereas the observed curvatures appear 

 to have been traumatic in origin. 



8 Errera, Bot. Ztg., 1884, p. 653; Wortmann, Bot. Ztg., 1887, p. 803; Steyer, Reizkriimmungen 

 bei Phycomyces nitens, 1901, p. 19. That only solid bodies act as stimuli was shown by Wortmann. 

 The sporangiophore of Fhycomyces responds most actively during the period of stretching growth, 

 but the weak power of reaction present just before the formation of the sporangium disappears with 

 the cessation of growth. 



