SLEEPING AND WAKING OF PLANTS. 5 



nutation, like the leaf C, which had preserved all the air naturally con- 

 tained in the air cavities, and which, for this reason, was also later 

 asleep and earlier awake than the two leaves A and B. Thus the 

 sleep of vegetables is prolonged in proportion as there is less air in the 

 air-organs. This, very probably, is one of the causes which vary 

 the hours of sleeping and waking of plants. We remark also in these 

 experiments, that the waking is more impaired than the sleeping by 

 diminishing the interior air of the plants. When the diminution of the 

 interior air is considerable, the sleep* is equally profound as in the 

 natural state, but the waking is incomplete. I have again tried the 

 effect of a vacuum produced by the air-pump on the flowers of vege- 

 tables, which exhibit the phenomena of sleeping and waking. I have 

 constantly seen that when a flower, either asleep or awake, is placed in 

 a vacuum, it invariably preserves the state in which it is placed there. 

 It is in vain that a flower placed in such circumstances is exposed to 

 the light, or even to the rays of the sun ; it never alters : the darkness 

 of night comes in vain; it has no power to promote sleep in the plant 

 which has been placed in a vacuum during its waking state. It is 

 therefore well established by experience, that the vacuum of the air- 

 pump, by withdrawing the air contained in the air cavities of plants, 

 deprives them entirely of the faculty of moving the floral organs, in 

 order to assume alternately the positions which constitute sleeping and 

 waking. We have seen that this privation of air divests them of the 

 faculty of moving, even when under the influence of anything that 

 stimulates plants possessing this quality, such as the sensitive plant. 

 By taking away the atmospheric air of plants, we suppress their exci- 

 tability, or the faculty which they possess in various degrees of being 

 affected by outward exciting causes, and of moving in consequence of 

 this influence. 



These experiments prove that the interior air is indispensably neces- 

 sary for exercising the alternate movements which constitute sleeping 

 and waking; and, in general, for the existence of the faculty, more or 

 less apparent in plants, of being affected by the influence of certain 

 exciting causes from without, and of executing the movements caused 

 by this influence. In this point of view, the action of oxygen on the 

 interior of plants appears to be very similar to the action of oxygen on 

 the interior of animals. Among plants, as well as animals, the priva- 

 tion of this interior oxygen destroys vitality, or, in other words, causes 

 asphyxia and death. 



