148 PLANTS WHICH EXHIBIT MOVEMENTS IN THE CAPTURE OF PREY. 
This change, known as “aggregation”, is propagated from the spot irritated down 
from one cell to another through the tentacle, across the leaf surface to adjoining 
tentacles, up to the heads of these, and so further and further radiating, so to speak, 
in all directions. Accompanying this visible sign of conduction, we have the 
bending of all tentacles in which the purple fluid is altered in the way described. 
When the source of excitation, the piece of flesh, is dissolved and digested, and the 
tentacles resume their original position, the dark lumps and spheres in the cavities 
= =e 
Fig. 27.—Venus's Fly-trap (Dionea muscipula). 
of the protoplasts disappear, and the homogeneous purple colour is restored as it 
existed before the stimulation. 
The various species of the Sun-dew genus are distributed over all parts of the 
world, and are more numerous than those of any other genus of the family of 
Droseracew. Most of the other genera belonging to this order (Dionea, 
Aldrovandia, Byblis, Roridula, Drosophyllum) are by no means rich in members. 
Each is represented merely by a single or few species, and is found exclusively in 
a very limited distriet. Like Drosera, they are all insectivorous plants, and all 
have the power of dissolving, absorbing, and using as supplementary nutriment, 
nitrogenous compounds from dead animals. The most striking of them are Dionea 
and Aldrovandia. They form the very small third group of animal-captors, in 
which movements are performed for the purpose of prey, and their apparatus for 
