SENSITIVE PLANT. 
301 
If a drop of aqua-fortis is placed upon a leaf so as 
to remain stationary, it does not affect the plant ; 
but when it begins to spread, the irritation is com- 
municated from one leaflet to another, till the whole 
of them on that part of the stalk are closed. The 
vapour of burning sulphur immediately deranges 
them, and the leaves will be affected, according as 
they are more or less exposed to the fumes. Al- 
though a branch of this extraordinary plant be di- 
vided through two thirds of its diameter, yet the 
leaves belonging to it retain the same degree of sen- 
sibility, and open and shut with the same freedom 
as before. This is the fact, though at the same 
time we must acknowledge it difficult to conceive 
how so great a wound can be made without pro- 
ducing any sensible alteration in the plant. 
The vapour of boiling water affects the leaves in 
the same manner as if they were burnt, and those 
which are exposed to its influence are benumbed for 
several hours, and seldom recover themselves en- 
tirely during the remainder of the day. 
Thus we have detailed the principal phenomena 
that occur in this very singular plant, upon which 
so many observations have been made. Many con- 
jectures have been formed, and many theories raised, 
to account in a satisfactory manner for the spring 
which works this delicate machine ; but as yet it 
has eluded the search of the naturalist, and the 
question will not probably be soon resolved. It has 
been supposed by some that the mimosa is endued 
with a power of perception which actuates all its 
