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. 
Linnaeus 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 ) 
