Plants are subject to attack and infection by a remarkable variety of symbiotic species and have
evoived a diverse array of mechanisms desigined to frustrate the potential colonists. These can be
divided into preformed or passive defense mechanisms and inducible or active systems. Passive
plant defense comprises physical and chemical barriers that prevent entry of pathogens ,such as
bacteria, or render tissues unpalatable or toxic to the invader. The external surfaces of plants, in
addition to being covered by an epidermis and waxy cuticle, often carry spiky hairs know as
trichomes, which either prevent feeding by in sects or may even puncture and kill insect larvae.
Other trichomes are sticky and glandular and effectively trap and immobilize insects.