4 SLEEPING AND WAKING OF PLANTS. 



of experiments upon indigenous vegetables. I shall mention some of 

 these. 



It is well known that the leaves of the kidney-bean have evident inter- 

 vals of sleeping and waking; they have besides a very remarkable nutation. 

 I was desirous of ascertaining by experiments, the effects produced on 

 these phenomena by withdrawing the interior air of the leaves. I took 

 three leaves of the kidney-bean, which I shall call A, B, C. The leaf A 

 was put into water, and kept during a quarter of an hour in vacuo : on 

 restoring it to the air, the air cavities were entirely filled with water. The 

 leaf B remained also a quarter of an hour in vacuo, but without hav- 

 ing been immersed. The leaf C remained in its natural state. I put 

 the stalks of these three leaves into vases filled with water, which I 

 exposed to a full strong light. In the evening, the leaf A first ex- 

 hibited the phenomenon of depressing its leafits, or of sleep ; the 

 leaf B presented this phenomenon later ; and the leaf C later still. 

 The next day, the leaf C first presented the phenomenon of straightening 

 its leafits, or of waking ; the leaf B next awoke ; and last of all the 

 leaf A. But the cessation of sleep in the two latter was incomplete ; 

 their leafits remained during the whole day in a state of drowsiness, 

 and they made no movement of nutation towards the light. The leaf 

 C, on the contrary, not only straightened its leafits completely, which 

 constitutes the act of waking, but it inclined the upper side towards 

 the window that admitted the light, which constitutes the act of nuta- 

 tion. On the evening of the second day, the leaf A was again the 

 first to show the phenomenon of sleep ; it was followed by the leaf B, 

 and lastly by the leaf C ; the latter ceased at the same time to keep the 

 upper side of its leaf- stalks inclined towards the window ; the nutation 

 ceased during the night, and the leafits resumed their natural position. 

 On the third day, the leaf A presented no symptoms of waking, and 

 began to wither; the leaf B revived in a trifling degree, but it con- 

 tinued drooping ; the leaf C, perfectly alive, performed its functions as 

 usual. On the fourth day, the leaf A was dead ; the leaf B began to 

 fade, and was dead the next day ; the leaf C continued to live some 

 time. 



These experiments demonstrate to us, that the sleeping and waking 

 of plants, and their nutation, depend on the air which is contained in 

 their air-organs, and is in proportion even to the quantity of that air. 

 The leaf A, the air-organs of which had been deprived of air, and 

 nearly filled with water, slept earlier and awoke later than the leaf B, 

 which having its air-organs deprived of air, had in the meantime 

 remained inaccessible to its return. These two leaves gave no signs of 



