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of the petiole, the cells of which constitute, as it were, two 
springs acting in contrary directions, so that if the one from 
any cause be paralysed, the other pushes the leaf in the direc- 
tion of least resistance. These springs, if they be so called, 
are set in action by the rush of fluid creating a turgid state of 
the one set of cells and an empty state of the other. What 
circumstances regulate the turgescence are only imperfectly 
known.” It will be obvious, that, even if this is correct as a 
statement of facts, it offers no real explanation of the pheno- 
menon ; for it is quite as difficult to understand how the mere 
approach of the hand, which gives rise to a sensitiveness com- 
mencing, it will be remarked, at the extremity of the leaf, 
will account for a 44 turgescence ” of the springs at the base of 
the leaf, which then causes the movement. It should be 
observed also that we are unaware of any use which these 
movements are to the plant. Similar sensitiveness occurs in 
the leaves of some other leguminous plants, in several species 
of Oxalis , &c. M. Bert has observed that the sensitiveness is 
destroyed by the continual application of chloroform, and also 
by placing the plant constantly in the dark or in green light. 
Similar movements to that of the Sensitive Plant, but 
occurring spontaneously, may be observed in other plants. 
Thus in the Desmodium gyrans or 44 Telegraph Plant,” some- 
times grown in our hot-houses, belonging to the same order, 
Leguminosge, the leaf consists of three leaflets, a large central, 
and two smaller side ones. The motion is especially observable 
in the small side leaflets, which on a warm summer’s day may 
be seen to rise and fall by a succession of jerking movements ; 
now stopping for some time, then moving briskly, always 
resting for a while in some part of their course, and starting 
again without apparent cause, 44 seemingly of their own will,” 
as Prof. Asa Gray remarks. The movement is not simply up 
and down, but the end of the moving leaflet sweeps more or 
less of a circuit. It is not set in motion by a touch, but 
begins, goes on, and stops, of itself. 
An exceedingly remarkable instance of sensitiveness occurs 
in the case of the 44 Venus’s Fly-trap ” of North Carolina, 
Dionoea muscipula , represented in fig. 2. The mid-rib of 
each leaf serves as a kind of hinge. When the inside of the 
blade of the leaf, or the fine bristles which grow on its surface, 
are touched by any foreign substance, the hinge suddenly 
closes, and if the intruding substance be a fly or other small 
object, it is immediately imprisoned as represented in the 
figure, the teeth on the margin of the leaf closing firmly upon 
one another like a steel trap, the sides of the trap then 
flatten down and press firmly upon the victim, and it now 
requires a very considerable force to open the trap. If nothing 
