THE WEB OF LIFE 283 



turn and even the plant may retaliate. Many plants are 

 full of deadly poison ; many are densely infiltrated with 

 crystals from which even snails turn aside ; many have 

 thorns and spines which though primarily expressions of 

 peculiarities of constitution are often secondarily protec- 

 tive ; many have moats and railings which entrap or ward 

 off unwelcome insect visitors ; and so on through a long 

 list. 



More actively retaliatory are the carnivorous plants, like 

 the butterwort (Pinguicula), which attracts insects to its 

 glistening glandular leaf and there digests them, like the 

 bladderworts (Utricularia) with their neat traps for water- 

 fleas, like the sundews (Drosera) with their finger-like 

 tentacles, like the pitcher-plants (Nepenthes and Sarracenia), 

 catching very passively, and Venus' s Fly-Trap (Dionced), 

 capturing very actively, and so forth. Here there is a 

 definite turning of the tables. 



A hint of the retaliatory power of the plant is familiar 

 in the stinging nettle (Urtica dioica), with its hairs contain- 

 ing formic acid, but the capacity reaches its climax in a 

 large member of the order Urticaceae, the ' stinging-tree ' 

 (Laportea), species of which occur in Japan, Eastern India 

 and Queensland. A light touch of a leaf produces a viru- 

 lent effect lasting for days or even months. The pain is 

 described by men who have been stung as maddening and 

 agonizing, and the effect on horses and dogs is also very 

 severe. The Australian species may attain a height of 

 10-15 feet and is said to emit a disagreeable odour. 



Inter -Relations of a Pitcher Plant. Let us take one 

 case in more detail. In studying one of the insectivorous 

 plants, the Spotted Trumpet-Leaf, Sarracenia variolaris, 

 whose long tube forms a very effective trap, Prof. C. V. 



