132 BRITISH PLANTS 
with stellate hairs, but their function is doubtful, since. 
as far as we know, no digestive fluids are poured out over 
the bodies of the victims. 
Our English fly-catchers are poor things compared 
with the insectivorous plants of the Tropics and the 
Southern Hemisphere. The mechanism of the pitcher- 
plant, Nepenthes, is one of the wonders of the vege- 
table world, while in 
Venus’s fly-trap, 
Dionea, the two halves 
of the leaf snap to- 
gether as soon as an 
insect touches one of 
the trigger-like hairs 
on its surface. 
4. Symbiotic Plants. 
(Gr. syn, together ; 
bios, life).— We have 
already considered one 
case of intimate asso- 
ciation between two 
living plants — the 
parasite and the host 
(p. 125). But in this 
case the advantage is 
entirelyone-sided. The 
parasite lives at the 
expense of the host; it 
takes everything, and 
gives nothing in return, 
A! In symbiosis, however, 
Gh sal two plants live to- 
Fic. 46.—Utricularia vulgaris (Buapper- gether, but the relation 
WORT), SHOWING BLaDDERS ON SUB- jg one of partnership, 
MERGED DissectED LEAVES AND . : 
sasentittag trours. both plants benefiting 
equally by the associa- 
tion. The most remarkable instance of symbiosis is 
the lichen, a dual plant, consisting of a fungus and an 
alga living together, and forming what appears to be 
one plant. The alga, being green, makes starch; the 
fungus makes use of this, and in return not only gives 
shelter and protection to the alga, but tenaciously stores 
up within its slimy walls a supply of water which keeps 
