I 2 6 MOVEMENTS OF CURVATURE 



The amplitude of the daily movements of Cassia marylandica decreases 

 on the klinostat, while the geotropic induction seems to overcome the 

 inherent physiological dorsiventrality of Desmodium gyrans> since Fischer 

 found the sleep - movements of this plant continue in the usual direction 

 on a klinostat, and Pfeffer found that in the inverted position they were 

 reversed. It is, in fact, only natural that intermediate conditions should 

 exist between strictly autonyctinastic and strictly geonyctinastic plants \ 



Owing to the induced periodicity the daily movements do not at 

 once cease on a klinostat, but continue for some days with decreasing 

 amplitude, and under normal conditions slowly regain their original value. 

 When a plant of Phaseolus is inverted, however, the dominating influence 

 of the geotropic induction causes the sleep-movements to be reversed on 

 the very first day. Since the curvature of the pulvinus influences not 

 only the geotropic induction but also the photonastic tone, the progress 

 of the movement exerts a certain modifying influence upon its continuance, 

 quite apart from any geotropic or heliotropic action. Stahl 2 , in dis- 

 cussing the subject solely from a biological standpoint, has unfortunately 

 not properly distinguished the tropic orienting movements from the 

 aitionastic ones. Indeed, the movements of the leaves on vertical branches 

 may differ slightly from those on more horizontal ones for a variety of 

 reasons 3 . Hitherto experiments have been performed only upon the 

 variation movements of pulvini, but it seems probable that similar relation- 

 ships will be found to hold good for the daily movements due to growth 4 . 



Dorsiventrality, whether morphological or physiological, usually in- 

 volves a more or less pronounced power of aitionastic reaction, and many 

 cases in which a labile or stable dorsiventrality is induced by unilateral 

 stimulation afford at the same time instances of the induction of photonasty, 

 thermonasty, and the like. Probably no tropic action leaves the power 

 of aitionastic reaction entirely unaffected, and Phaseohts affords a good 

 instance of the reversal or induction of the power of photonastic response 

 by geotropic action. Although in this case the induction is coupled with 

 a geotropic curvature, nevertheless in other cases pronounced structural 

 induction may take place without any special motile response. The 

 structure, however, affords no indication of the existence of a power of 

 aitionastic, tropic, or other irritability, and hence the photonastic irrita- 

 bility of the pulvinus of Phaseolus may be induced or reversed without 

 the dorsiventral structure of the pulvinus experiencing any perceptible 

 alteration. 



1 A. Fischer, 1. c., p. 711. The term autonyctinastic is employed here in preference to that of 

 autonyctitropic. According to Fischer (1. c., p. 709), Mimosa pudica is also autonyctinastic, but it is 

 not stated whether the evening fall of the primary petiole continues on the klinostat. 



Stahl, Bot. Ztg., 1897, p. 86. 



8 Darwin, The Power of Movement in Plants, 1880, p. 263. 



4 Cf. Pfeffer, 1. c., p. 143. 



