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: 
ON LEAVES. 95 
when he substituted for the water a drop of sulphuric acid, he 
observed that the folioles shrivelled up, the partial petioles as well 
as the common petiole was lowered, and gradually submitted 
to its influence, without the folioles situated below participating at 
all in the movement. This ‘experiment shows very clearly that 
the irritation is not local, but communicates from circle to circle 
in the various elements of a leaf, and propagates itself from one 
leaf to another. : 
During the time that these movements are in operation, it will 
be observed that the limb of the foliole neither curves itself nor 
shrivels. In short, the contractile power resides at the point of | 
SSS QOH, 
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LS eA we i ‘ 
i“ or Z 
Fig. 123.—Branch of the Sensitive Plant. 
insertion of the folioles upon the secondary petioles, these upon 
the common petiole, and these again upon the stem. These various 
points of insertion correspond to the very perceptible cylindrical 
cushions which during the season of rest swell below, while in the 
state of irritation they are distended above. The movement 
which we provoke in the case of the Sensitive plant manifests itself 
with much greater rapidity when irritated upon this cushion than 
in any other part of the plant. 
We have remarked that the more vigorous the Sensitive plant is 
in its habit, the more susceptible is it; the higher the temperature, 
the more promptly does it respond to the touch. We may observe 
besides that the Sensitive plant can, up to a certain point, get 
accustomed to the movement. Desfontaines, carrying a Sensitive 
