THE DIAL OF FLOWERS. 



Certain plants possess the remarkable property of 

 opening and shutting their flowers at particular seasons. 

 Some, for example, open them all day, while others ex- 

 pand them only in the evening. There are likewise noc- 

 tiflorous plants, which close their flowers in the morning. 



In the above cases the degree of heat might be alleged 

 as the exciting cause of the expansion of flowers ; but this 

 will not hold good- with regard to other vegetables, which 

 open and shut their blossoms at stated hours of the day, or 

 at certain distances of time before change of weather. In 

 these latter cases we must look for some other cause of 

 the phenomenon, perhaps to some electrical changes in the 

 state of the atmosphere. 



Linnseus has enumerated forty-six flowers which possess 

 this kind of sensibility : he divides them into three classes. 

 1. Meteoric Flowers, which less accurately observe the 

 hour of folding, but are expanded sooner or later accord- 

 ing to the cloudiness, moisture, or pressure of the atmo- 

 sphere. 2. Tropical Flowers, that open in the morning 

 and close before evening every day, but the hour of their 

 expanding becomes earlier or later as the length of the 

 day increases or decreases. 3. Equinoctial Flowers, which 

 open at a certain and exact hour of the day, and for the 

 most part close at another determinate hour. 



(211) 



