DIAL OF FLOWERS. 
Certain plants possess the remarkable pro¬ 
perty of opening and shutting their flowers at 
particular seasons. Some, for example, open 
them all day, while others expand them only 
in the evening. There are likewise noctiflorous 
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 expan¬ 
sion of flowers : but this will not hold good 
with regard to other vegetables, which open 
and shut their blooms 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 pheno¬ 
menon, 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 according to the cloudiness, moisture, 
or pressure of the atmosphere. 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. 
