148 



PLANTS WHICH EXHIBIT MOVEMENTS IN THE CAPTURE OF PP.EY. 



This change, known as "aggregation", is propagated from the spot irritated down 

 from one cell to another through the tentacle, across the leal' 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 pui'ple 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 



^Ä^>:^^t5.^^ 



1 :^m^-M^^^&^W^'^'^- 



Fig. 27. — Venus's Fly-trap {DioncBa mru--^ipuUt)- 



of the protojjlasts disaj^pear, 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 

 Droseracea3. Most of the other genera belonging to this order (Dionau, 

 Aldrovandia, Bijlilis, Rorldula, Drosophyllum) are by no means rich in membei"S. 

 Each is represented merely by a single or few species, and is found exclusively in 

 a very limited district. Like Drosera, they are all insectivorous plants, and all 

 have the power of dissolving, absorbing, and using as supplementär}- nutriment, 

 niti'ogenous compounds fn.mi dead animals. The most striking of them are Dioncea 

 and Aldrovandia. Thej^ form the very small third group of animal-captors, in 

 which movements are performed for the purpose of pi"ey, and their apparatus for 



