Page:An introduction to physiological and systematical botany (1st edition).djvu/359

 Rh, and others, while the over-shadowing corolla keeps off rain, the air has free access underneath to blow the pollen to the stigma. Nor is this drooping caused by the weight of the flowers, for the fruit in most of them is much heavier, and yet stands erept on the very same stalk. The papilionaceous flowers in general spread their wings in fine weather, admitting the sun and air to the parts within; whereas many of them not only close their petals at night, but also derive additional protection from the green leaves of the plant folding closely about them. Convolvulus arvensis, t. 312, Anagallis arvensis, t. 529, Calendula pluvialis, and many others, are well known to shut up their flowers against the approach of rain; whence the Anagallis has been called the Poor Man's Weather-glass. It has been observed by Linnæus that flowers lose this fine sensibility, either after the anthers have performed their office, or when deprived of them artificially; nor do I doubt the fact. I have had reason to think that, during a long continuance of wet, the sensibility of the Anagallis is sometimes exhausted; and it is