PROFESSOR MACAIRE ON THE DIRECTION ASSUMED BY PLANTS. 
275 
the dark and in the light. The rays of the sun are not indispensable ; and the expe- 
riment, which is easy to perform and pleasing to witness, succeeds very well in dif- 
fused light. 
I have ascertained that some other leaves, among others those of the Laurus thy- 
mus, Portugal laurel, &c., give similar results. 
In conclusion, I have endeavoured to show: — 
1st. That light is the only agent in the turning over of leaves. 
2nd. That it does not act by a physical attraction properly so called. 
3rd. That the turning over of leaves takes place sometimes by a torsion of the 
footstalk, sometimes by a curling of the flat part of leaves. 
4th. That the blue rays appear to be the most, and the red the least active in 
effecting the turning over of leaves. 
.5th- That the exhalation of leaves is much increased when their under surface is 
exposed to light. 
6th. That the decomposition of carbonic acid and the disengagement of oxygen 
gas are, under the same circumstances, considerably diminished. 
2 o 
MDCCCXLVIII 
