LEAVES WITH BEGABD TO LIGHT. 



443 



the normal position and not on the klinostat, these two would 

 have remained above the horizon ; being, however, on the kli- 

 nostat and freed from the influence of apogeotropism, they 

 became epinastically bent like the leaf iii., which pointed 

 towards the light, and whose original angle beneath the horizon 

 was much increased; leaf ii. grew out parallel to the glass 

 of the window — that is, halfway between those which pointed 

 towards and those which pointed away from the light ; its epi- 

 nastic curvature was also large *. 



Experiment 6 (Table XV.)- — In another similar experiment, the 

 leaf which was pointing away from the light, and which was above 

 the horizon, remained in this position when the plant was placed 

 on the klinostat, while the leaf which pointed to the light, and was 

 below the horizon, became strongly curved. The following table 

 gives the angles. 



Table XV. 



Date. 



i. 



Lamina. 



ii. 

 Lamina. 



May 17, 9.25 a.m.... 

 May 18, 10.30 a.m.... 

 May 19,9.40 a.m.... 



+55 

 +55 

 +55 



o 



- 11 



- 65 

 -118 



The plant was fixed on the klinostat in the lateral position 

 May 17th, 9.25 a.m., and the angles immediately taken. Leaf i. 

 pointed away from the window, so that its upper surface was di- 

 rected towards the light. It must not be supposed that the 

 non-curvature of leaf i. resulted from any loss of epinastic power 

 in its petiole ; for after the observations recorded on May 19th 

 the plant was removed from the klinostat, and on May 20th 

 it was placed in the normal position, but in a reversed posi- 

 tion as regards light ; that is, leaf i. was made to point towards 

 the light : under these circumstances it became curved, and 

 was at 8° below the horizon on May 22nd, and 40° beneath it on 

 May 24th. 



It seems, therefore, that the stimulus of light was sufficient in 



* It is hardly necessary to state that, in all cases where it was necessary, the 

 heliotropic curvatures of the stem were prevented by tying it to a stick fixed in 

 the pot. 



