In this article we will discuss about the defensive mechanism in plants.
1. Very often plants are provided with hard sharp-pointed bodies which serve as weapons for self-defence. They may be morphologically different, but all of them carry on the same function. Thorns are the pointed organs, as found in Duranta (B. Mehdi).
These are metamorphosed stems. Leaves or parts of leaves are also modified into sharp-pointed bodies, as in date- palm and Cactus. They are called spines. Roses and canes usually bear curved outgrowths on their bodies for the same purpose. They are prickles.
2. Formation of dense hairs on the surface of the organs, as a check against attacking animals is quite common in plants. Glandular hairs of Jatropa (B. Bheranda), Plumbago (B. Cnita), etc., secrete sticky substances which adhere to the mouths of the grazing animals and make them uncomfortable.
The stinging hairs of nettles and Mucna (B. Alkusi) are nice examples of defensive mechanism in plants. These hairs are long and have sharp brittle tips. As soon as they come in contact with animals, the tips break and make pricks or punctures on the skin of the animals. Immediately a fluid is secreted by the gland lying at the basal region, which is injected, so to say, on the animal and creates the irritation.
3. During metabolic activities various waste products are formed in the plants. Alkaloids found in Cinchona, Nux-vomica, poppy, tobacco, the milky juice, latex, present in many plants; different types of crystals, particularly the needle-shaped crystals of calcium oxalate occurring in different varieties of aroids, are the common waste products which become helpful in warding off the animals.
Besides these, many plants have bitter and disagreeable taste, e.g. bitter gourd, and repulsive odour, as in Typhonium (B. Ghet Kachu), and are thus avoided by the animals.
4. Some plants escape the attacks of the animals by imitating some dangerous animals like the venomous snakes. A common Aroid known as Arisaema or snake plant, possesses a greenish purple spathe which expands over the spadix in such a manner that it looks like the hood of a cobra (Fig. 75). Such phenomenon is known as mimicry.
5. Plants like mango often give shelter to various types of ants and other stinging insects which act as an army, and protect the plant whenever necessary. Such an adaptation is called myrmecophily.
