66 VITAL FUNCTIONS OF PLANTS. [LECT. II. 



tables, in common with animals, possess vital 

 energy, which distinguishes them from inert matter, 

 and displays itself by its effects. If we wish to 

 extend the inquiry beyond the examination of these 

 effects, and demand what vitality is ? we are forced 

 to pause, and acknowledge the inefficacy of human 

 means to unveil those mysteries which the Author 

 of nature chooses to conceal. We know that vi- 

 tality is attached to organization ; but it does not 

 depend on structure : it is not caloric, the cause of 

 heat, although with this agent it has the closest 

 possible connexion : nor is it chemigal affinity, for 

 it resists in organized bodies those combinations 

 which affinity produces among their components 

 when vitality ceases. The flights of imagination 

 fail us in forming any conjectures as to its nature ; 

 we search in vain for a solution of the question in 

 the schools of Philosophy; reason avails us nothing; 

 and we are forced to contemplate its effects in si- 

 lent admiration, and to regard it as an impulse of 

 the Divinity, breathed upon the organized part 

 of the creation, astonishing and incomprehen- 

 sible. 



Another principle which vegetables possess in 

 common with animals, and which depends on life, 

 is irritability, or the susceptibility of being acted 

 on by external stimulants, so as to produce a change 

 in the parts, or the relative situation of the parts 

 of the body, \diich, without the impression thus 

 communicated, would not have taken place. Those 



