436 



ME. F. DABWTN OK THE POSITION OF 



Table VIII. 



Date. 



Leaf i. 



Leaf ii. 



Lamina. 



Petiole. 



Lamina. 



Petiole. 



April 2, "I 

 10.52 a.m. j 



April 3, | 

 9.30 a.m. j 



April 5, 1 

 4.25 p.m. J 



April 7, 1 



11.21 A.M.) 



+90* 

 + 5 

 -12 

 -15 



o 

 +80 



+63 



+22 chd 



+20 chd 



O 



+70 

 + 57 

 +25 

 +52 



o 



+ 80 

 +74 

 +40 

 +52 



The angles here given were measured by stopping the klinostat when the 

 plant was in the normal position, and measuring the angles above (+) and 

 below ( — ) the transverse plane, 1 1. The axis of rotation and the direction of the 

 light being parallel to 1 1, the leaves will be at right angles to the light when 

 leaf i. is at -90°, and leaf ii. at+90°. 



should be noted that in the case of i. it cannot be tbe absence of 

 apogeotropism which caused the failure to reach the diaheliotropic 

 plane, since epinasty unopposed by apogeotropism would tend 

 to bring it more easily into that position than if gravitation were 

 acting on it. It is also clear that ii. could not have remained in 

 its final position if it were dependent on apogeotropism ; and it is 

 therefore certain that some other force arrested the epinasty 

 of n. This experiment ought to be compared with the result 

 of absolutely lateral, i. e. not oblique, illumination on a plant of 

 Ranunculus Ficaria growing under the influence of gravitation 

 m the normal position ; but this unfortunately was not done. 

 The results of experiments 7 and 8 show clearly that a leaf can 

 move either in the epinastic or hyponastic directions, and that 

 these movements are produced and checked by the stimulus of 

 light, and without the stimulus of gravitation, in such a way that 

 a plant tends to place its leaves at right angles to the light, though 

 it may not perfectly succeed in doing so. 



Experiment 9.— These observations show the effect of illumi- 

 nating the under surfaces of the leaves. 



Table IX. 



Date. 



Leaf i. 



Leaf ii. 



April 2, 11 a.m 

 April 5, 4.30 p.m.... 

 April 7 



Lamina 



o 



- 45 

 -110 



- 90 



Lamina. 



O 



- 35 

 -120 



- 80 





