82 MOTION IN 
Bat in some of the species of Mimosa or Sensitive 
Plants, the slightest touch of the hand will produce 
a sudden and very considerable change in the posi- 
tion of the leaves, as they will immediately fold them- 
selves together, and if the touch be repeated, the 
leaf-stalks will fall and bend themselves toward the 
stem. A strong wind or heavy rain will produce the 
same effect, and those kinds which grow in countries 
where there is a long continuance of rain, close their 
leaves upon its approach, and are seldom fully ex- 
panded until the return of fair weather. 
The leaves of the common sensitive plant will par- 
tially close at evening, and remain so until the light 
of day again causes them to expand; and when ex- 
posed to sudden cold during the daytime, they will 
fold themselves face to face, so as to allow as little as 
possible of the upper surface to remain open to the 
air. 
The Venus Fly-trap is also an example of motion; 
the leaves are very curiously constructed. At the 
extremities are spread out two wide and rounded 
lobes, each armed upon the margin with rows of 
spines, or rather stiff hair-like processes, locking 
into each other when they meet, which always occurs 
when irritated. The upper surface of these lobes is 
covered with minute glands, which evidently con- 
tain a liquid attractive to insects, as they fre- 
quently resort to the plants; but no sooner do they 
alight upon the leaves, and their little feet irritate 
them, than the two lobes instantly fold together, 
squeezing the insect to death. The leaf seldom opens 
