266 THE WONDERS OF VEGETATION. 



that closed their leaves at night to an artificial light, 

 little inferior in brilliancy to that of day. " When 

 I exposed these plants to light by night, and placed 

 them in obscurity by day," he says, " they opened 

 and closed their leaves at first without any fixed 

 rule ; but after a few days they adapted themselves to 

 the new condition of things, and accepted night for 

 day and day for night ; opening their leaves with reg- 

 ularity at night, which now brought them light, and 

 closing them during the daytime. When I exposed 

 them to continuous light, day and night, they had, as 

 in the ordinary state of things, alternate seasons of 

 sleeping and waking ; but these seasons were some- 

 what shorter than in nature. When I exposed them 

 to continual darkness, they also slept and remained 

 awake alternately, but the intervals were very irreg- 

 ular." 



The natural inference from these facts is that this 

 tendency towards periodic motion is inherent in the 

 plants ; and that light, acting with different degrees of 

 intensity upon different species, is the chief cause of 

 it. It must be added, however, that other botanists 

 have failed to obtain the same results as Linnaeus and 

 De Candolle ; so that the question is not yet absolute- 

 ly decided. It is claimed by many naturalists, that 

 there exists a hidden bond which connects the life of 

 plants with the great luminary in the heavens. 



