a. Doctrine of signature :

• The doctrine of signatures is a theory in old natural philosophy that states that herbs resembling various parts of the body can be used by herbalists to treat ailments of those body parts.
• For example, eyebright was used for eye infections, owing to the supposed resemblance of its flower to an eye.
• The doctrine was based on the belief that God would have wanted to show men what plants would be useful for. However, it is today considered to be pseudoscience and has led to many deaths and severe illnesses.

b. Ethnobotany: It is the study of the relationship between plants and people and their culture.

c. Pharmacognosy:

• Pharmacognosy is the study of natural products from various sources that have potential medicinal or health benefits.
• It involves the physical, chemical, biochemical and biological properties of drugs, drug substances or potential drugs from natural origin, as well as the search for new drugs from natural sources.
• Pharmacognosy also covers the study of natural product molecules that are useful for their ecological, gustatory or other functional properties.

d. Pharmacology:

• Pharmacology is a branch of medicine, biology, and pharmaceutical sciences concerned with drug or medication action.
• It deals with the research, discovery, and characterization of chemicals which show biological effects and the elucidation of cellular and organismal function in relation to these chemicals.

e. Pharmacopeia:

• Pharmacopeia is a word that means “drug-making” or “to make a drug”.
• It is also a book that contains directions for the identification of compound medicines, and is published by the authority of a government or a medical or pharmaceutical society.

f. Phytochemistry:

• It is the study of phytochemicals produced in plants, describing the isolation, purification, identification, and structure of the large number of secondary metabolic compounds found in plants.

g. Phytotherapy:

• It is the use of plants extracts for medicinal purposes.