CHAP. XIV. 
DIRECTIONS TAKEN BY ORGANS. 
417 
alteration took place in its position. Now, as, from Bonnet’s 
experiments, it is certain that leaves immersed in water act 
exactly as if surrounded with air, it is to be inferred that the 
external influence of the light is of no effect, unless aided by 
a spontaneous power within the vegetable, which was destroyed 
by the removal of the petiole. Leaves immersed in water 
under similar circumstances, with their petioles and stem un- 
injured, turned towards the light as they would have done in 
the open air. 
I am unwilling to give more space to this subject, which 
belongs less to practical physiology than to speculative phi- 
losophy. The reader who wishes to study it will find abun- 
dant illustrations, explanations, and speculations in Dutrochet’s 
Memoires pour servir a V Histoire Anatoinique et Physiologique 
des Vegetaux : Paris, 1837. 
