CHAP. 5. 2. ON VITAL FUNCTIONS. 197 



The Hypochaeris radicata, Hieradum Pilo- 

 sella, and several others of this family, shut 

 their flowers about three o'clock in the after- 

 noon. 



The Four o'Clock Flower is also well known, 

 and is nearly as regular as a watch. 



The Pimpernel, Anagallis arvensis, does not 

 open its flowers in the morning when JJain is 

 coming, and has become thereby an indicator 

 of the ensuing weather. 



Hence there seems to be some particular 

 periodical influence exerted on certain plants in 

 the course of the day, and on others casually, 

 in particular weather. In general I have re- 

 marked that the syngenesious and composite 

 flowers are most under the influence of the 

 former. What this influence -consists in is 

 unknown ; neither has any conjecture been 

 made, unless that of the electric state of the 

 air varying at stated periods of the day ; but 

 the phaenomenon should be more attended to ; 

 and the question I beg to submit to future 

 observation is : whether any connexion can be 

 found between the times of these vegetable pe- 

 riods discovered in the phaenomena of plants, 

 and those periods of the recurrence of the 

 paroxysms of ephemeral diseases observed 



