298 
SENSITIVE PLANT. 
heavily, and is accompanied with wind, the plant 
immediately becomes affected. 
The leaves which have been irritated and made 
to close, at length recover themselves and resume 
their former position. The time necessary to effect 
this purpose is unequal, since it depends on differ- 
ent circumstances, such as the health of the plant, 
the season of the year, the hour of the day ; some- 
times it is effected in twenty minutes, sometimes in 
less than ten. The order also in which this is ma- 
naged, is subject to vary ; sometimes it begins in 
the leaves on the sides of the leaflets, sometimes in 
the branches, and then the whole of the plant is 
generally included in the motion. 
It is said in the Histoire de /’ Academie des 
Sciences , for the year 1729, that in a dark place, and 
in a uniform temperature, the mimosa never fails to 
observe two periodical motions, that is, to shut up 
its leaves at night, and open them again in the 
morning. The following experiment, however, 
made by Dufay and Duhamel, does not appear 
to confirm this observation — “ A sensitive plant 
being carried in the month of August into a dark 
cave, where the temperature of the air was more 
equal than in the place appropriated to the former 
experiment, the plant indeed closed its leaves ; but 
it was, in all probability, occasioned by being shook 
in the carnage. It did not recover itself till about 
twentv-four hours afterwards, and from that time 
continued open during three days, though not quite 
so much so as when in a perfectly natural state. 
