420 
PHYSIOLOGY. 
BOOK II 
111 Others the leaves converge over the floivers, as if to 
shelter those most delicate organs from the chill air of night. 
The flowers of the Crocus and similar plants expand beneath 
the bright beams of the snn, but close as soon as they are 
withdrawn. The (Enotheras unfold their blossoms to the 
dews of evening, and wither away at the approach of day. 
Some Silenes roll up their petals in the day, and expand them 
at night. The florets of numerous Compositas, and the petals 
of the genus Mesembryanthemum, are erect in the absence 
of sun, but become reflexed when acted upon by the sun’s 
beams; and many other such phenomena are familiar to every 
observer of nature. It is probable, indeed, that a different 
effect is produced upon all plants by day and night, although 
it is less visible in some than in others ; thus plants of Corn, 
in which there is little indication of sleep when grown singly, 
exhibit that phenomenon very distinctly when observed in 
masses ; their leaves become flaccid, and their ears droop at 
night. These effects have been generally attributed to the 
action of light ; and it is probable that that agent contributes 
very powerfully to produce them ; for a flower removed from 
the shade will often expand beneath a lamp, just as it will 
beneath the sun itself. De Candolle found that he could 
induce plants to acknowledge an artificial day and night, by 
alternate exposure to the light of candles. There must, how- 
ever, be some cause beyond light, of the nature of which no 
opinion has yet been formed; many flowers will close in the 
afternoon while the light of the sun is still playing upon 
them, and the petals of others will fold up under a bright 
illumination. 
Spontaneous movements are far more uncommon than those 
which liave just been described. In Megacliniuni falcatum, 
the labellum, which is connected very slightly with the 
columna, is almost continually in motion ; in a species of 
Pterostylis, shown me by Dr. Brown, I observed a kind of 
convulsive action of the labellum ; the filaments of Oscilla- 
torias are continually writhing like worms in pain ; several 
Confervas exhibit spontaneous movements in their spores : 
but the most singular case of the kind is that of Hedysarum 
gyrans. “ This plant has ternate leaves : the terminal leaflet. 
