CHAP. XIII. 
IRRITABILITY. 
349 
irritated, the sides collapse, so as to cross the ciliae of their 
margin, like the teeth of a steel-trap for catching animals. 
Roth is recorded to have seen something of the same kind in 
Drosera rotundifolia. If the bottom of the stamens of the 
common berberry is touched on the inside with the point of 
a needle, they spring up against the pistillum. The valves of 
Impatiens noli-tangere, when the fruit is ripe, separate and 
spring back with great elasticity when touched. In this case 
the phenomenon is apparently capable of explanation upon 
a similar principle to the Momordica elaterium. In the 
fruit of Impatiens the tissue of the valves consists of cellules 
that gradually diminish in size from the outside to the inside ; 
and the fluids of the external cellules are the densest. The 
latter gradually empty the inner cellules and distend them- 
selves ; so that the external tissue is disposed to expand, and 
the internal to contract, whenever any thing occurs to destroy 
the force that keeps them straight. This at last happens by 
the disarticulation of the valves, the peduncle, and the axis ; 
and then each valve rapidly rolls inwards with a sudden 
spontaneous movement. Dutrocliet proved that it was pos- 
sible to invert this phenomenon by producing exosmose : for 
that purpose he threw fresh valves of Impatiens into sugar 
and water, which gradually emptied the external tissue, and, 
after rendering the valves straight, at length curved them 
backwards. 
The column of the genus Stylidium, which in its quiescent 
position is bent over one side of the corolla, if slightly 
irritated, instantly springs with a jerk over to the opposite side 
of the flower. In Kalmia the anthers are retained in little 
niches of the corolla ; and, as soon as they are by any cause 
extricated, the filaments which had been curved back recover 
themselves with a spring. In certain orchideous plants, of 
the tribe called Vandeae, the caudicula to which the pollen 
masses are attached will often, upon the removal of the anther, 
disengage themselves v/ith a sudden jerk. 
An elaborate exposition of the phenomena accompanying 
the movements of the sensitive plant has been given by 
Dutrochet, in his Mecherches, Sfc. sur la Structure intime des 
Animaux et des Vegetaux^ et sur leur Motilite^ which should be 
