422 
PHYSIOLOGY. 
BOOK II, 
is, perhaps, the most familiar instance : but many others also 
exist. If any one of six bristles planted perpendicularly upon 
the leaf of Dionaea muscipula is irritated, the sides of the leaf 
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 themselves ; 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. 
Dutrochet proved that it was possible to invert this pheno- 
menon by producing exosmose: for that purpose he threw 
fresh valves of Impatiens into sugar and w^ater, which gradu- 
ally 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 irri- 
tated, 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 orchidaceous plants, of 
the tribe called Vandeae, the caudicula to which the pollen 
masses are attached will often, upon the removal of the anther, 
disengage itself with a sudden jerk. 
For numerous observations upon other cases of vegetable 
irritability, see Dutrochet’s Memoires previously quoted, in 
