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, 

 Dioncea, the two halves 

 of the leaf snap to- 

 gether as soon as an 

 insect touches one of 

 the trigger-Kke hairs 

 on its surface. 



4. Symbiotic Plants 

 (Gr. syn, together ; 

 hios, 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 Hves at the 

 expense of the host ; it 

 takes everything, and 

 gives nothing in return. 

 In symbiosis, however, 

 two plants hve to- 

 gether, but the relation 

 is one of partnership, 

 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 



Fig. 46. — Vtricvlaria vulgaris (Bladdbe- 

 wobt), showing Bladders on Sub- 

 merged Dissected Leaves aud 



ABSENCE OF RoOTS. 



