This module concerns with medicinal plants. Angiosperms are the original source of most plant medicines. The plants have the ability to synthesize a wide variety of chemical compounds which are used to perform important biological functions, and to defend against attack from predators such as insects, fungi and herbivorous mammals. Many of the herbs and spices used by humans to season food also yield useful medicinal compounds. The use of herbs and spices in cuisine developed in part as a response to the threat of food-borne pathogens. Further, the spices with the most potent antimicrobial activity tend to be selected. This module includes such topics as: Studies of Chemical Compounds of Plants which are of Value in Medicine; the Sources of Plant Drugs; and the Therapeutic Classes of Drugs.