The herbivores are predators of plants and nearly 25% insects are phytophagous (feeding on plants). So, plants show morphological as well as chemical defense against herbivores such as
(i) Thorns of rose and Acacia as well as cactus.
(ii) Certain plants produce chemicals, such as opium, quinine, caffeine, nicotine, etc., to protect them against being grazed by the animals.
(iii) Calotropis produces highly poisonous cardiac glycosides. So, the cattle and goats do not eat this plant.