LEAVES WITH REGABD TO LIGHT. 



433 



words, tbey bend backwards away from the source of light and 

 towards the diaheliotropic plane (see p. 429). Leaf ii. was 23° 

 behind the diaheliotropic plane on April 30th ; but by May 4th 

 this angle had again diminished to —5°. 



In the foregoing experiments all the leaves on a given plant 

 have behaved in a similar manner. In the following experiment 

 we have experiments 1 and 3 repeated on a single plant. 



Experiment 5. — A plant having been subject to lateral illumi- 

 nation, was placed April 7th, 11.30 a.m., in the zenith position. 



Table V. 



It will be seen that on April 9th leaf i., which had been far in front 

 of the diaheliotropic f plane, had begun to move back towards 

 it, and leaf ii. had begun to move from behind the transverse 

 plane also towards it. The plant had to be removed and refixed 

 on the klinostat, so that both leaves were brought 5° nearer 

 the transverse plane. By April 14th the lamina of i. was at 

 about the same angle (+20°), thougli the petiole had bent back- 

 wards. Both lamina and petiole of ii. had reached and remained 

 in the diaheliotropic plane. 



Experiment 6.— Another similar experiment may be given. 

 A plant which had been exposed for some days to a lateral illu- 

 mination was (April 2nd, 3.45 p.m.) placed in the zenith posi- 

 tion. 



* The plant was removed at 11 a.m. April 9, and replaced not exactly in the 

 same position. 



+ When a plant is in the zenith position, the diaheliotropic plane coincides 



with the transTerse plane. 



