CONJOINT EFFECTS 



125 



duction l . When such plants are inverted or rotated on a klinostat the 

 absence of the geotropic stimulus or its reversal causes the position of 

 the leaves to alter. This takes place with such rapidity in the case of 

 Phaseolus multiflorus and P. vnlgaris that when the plant is inverted, 

 a leaf in the day position passes in the course of a few hours into a position 

 resembling that assumed during night (Fig. 33, a and b). The pulvini still 

 perform photonastic curvatures, but these now take place in the opposite 

 direction in regard to the plant. 



Similar changes are shown by Desmodium gyrans, although in the 

 inverted position the 

 terminal leaflet does 

 not quite reach the 

 same angle as under 

 normal conditions. In 

 most pulvini, however, 

 the dorsiventrality is 

 fixed to such an ex- 

 tent that after inver- 

 sion the sleep-move- 

 ments retain the same 

 direction in regard to 

 the plant as before. 

 Fischer 2 has shown 

 that the same is the 

 case when the geotro- 

 pic action of gravity 

 is eliminated by rota- 

 tion on a klinostat. 

 Under these condi- 

 tions the sleep-move- 

 ments of Phaseohis 

 vulgar is, P. multi- 

 florus, and Lupinus 

 albus cease mainly 

 or entirely, so that the pulvini of these plants are physiologically radial 

 to photonastic stimuli in the absence of any geotropic induction. On the 

 other hand, in most plants such as Acacia lophantJia, Trifolimn pratense, 

 Amicia, and Biophytum sensitivum the photonastic reaction is mainly the 

 result of an inherent physiological dorsiventrality, since the sleep-move- 

 ments continue on a klinostat with considerable amplitude and in the same 

 direction as before. 



FIG. 33. In\ erted plant of Pkaseolus multiflorus. The petioles of the first 

 pair of foliage-leaves are fixed by the wire d, so that only the pulvinus at the 

 base of the lamina is able to curve. The leaf a is in the day position, while 6 is 

 shown in the night position. The leaflets of the trifoliate leaf c are brought into 

 the normal light position by the curvature of the basal pulvinus, and hence 

 carry out the normal sleep-movements. 



1 Pfeffer, Period. Bewegungen, 1875, p. 138. 



" Fischer, Bot. Ztg., 1890, p. 672. 



