Herbivory

• physical defences

  thorns, spikes, hairy leaves, inedible tissues
• alkaloids

  bitter tasting nitrogenous compounds

  affect metabolism, can be poisonous

  eg caffeine, nicotine, morphine, cocaine
• pheromones

  affects social behaviour of its species

  maple tree: releases pheromone, absorbed by others leaves, produce calls to protect from attack
• volatile organic compounds

  produced when plant detects attack by pest

  eg cabbages attract parasite to infect caterpillars, apple trees attract predatory mites
• may also fold in response to touch

  not usually visible, except in a few species