Plants are an integral part of nature and the nature reflects the creative powers of God. The plants are designed with a specific purpose. The physical beauty of plants and its chemistry, are of immense importance to humankind. They are the life sustaining forces on earth. The planet Earth is estimated to have originated about 4.7 billion years ago. The first prokaryotic organism evolved about 3.5 billion years ago and the eukaryotic cell appeared on the earth about 1.5 billion years ago as per the radioactive dating. The land plants appeared for the first time in the Silurian period of the geological time scale, about 425 million years ago. The flowering plants which form a major part of the cultivated crops and other useful plants, however, appeared much later in late cretaceous period about 65 million years ago and suddenly dominated the paleo forests during the tertiary, quarternary and recent geological periods. The primitive human being (Pithecanthropus erectus) appeared on earth during the middle to upper pleistocene period, also known as Paleolithic period. Through various stages of evolution, he reached a stage of modern specie (Homo sapiens) about 40,000 - 30,000 B.C and got spread through out the world within the next 10,000 - 20,000 years. During this period, he developed the ability to make fire and various kinds of tools in response to the need for mastering the environment, primarily for the quest for food. He gradually began cultivating plants and domesticating animals. Archaeologically, the period consisting of the last 10,000 years B.C. has been divided into prehistoric, protohistoric and historic periods. The man-plant relationship during the prehistoric and protohistoric period, has been reconstructed mostly on the evidence of plant remains and other associated articles used by man which have been recovered from archeological excavations. The neanderthal burial place in Iraq some 60,000 years ago, point out the use of several plants (Pandey and Chadha, 1997). The history of medicine and surgery dates back, perhaps, to the origin of the human race. But, as no mode of recording events existed in prehistoric times, there are no data on the methods of treatment practiced during that period (Jain, 1987 & Jain and Defillips, 1991). In those days, the subject of human suffering and its alleniation was intimately associated with religion, myth and magic (Choudhary Rai and Pal, 1975). India is rich in traditional knowledge. Vast ethnobotanical knowledge exists in India from ancient times. Written records on the use of plants for curing human or animal diseases in India can be traced back to the earliest scriptures of the Hindus, the Rigveda (4,500-1,600 B.C.). The Hindu period of medicine has been classified into four categories viz. 1. Vedic period 2. Period of agreement and research 3. Period of compilation and tantras and siddhas 4. Period of decay and recompilation (Chopra et.el,1958).The identity of several plants referred in the Suktas of the Rig Veda, can be fixed with reasonable certainity, e.g. of Semal, Pithavan, Palash and Pipal (Sharma and Goswami, 1992). Ayurveda, the Indian indegenous system of medicine dating back to the Vedic ages (1500-800 B.C.), has been an integral part of Indian culture. The Vedic Aryans were familiar with medicinal plants. Several plants are described in the Atharva Veda. (Mitra and Jain, 1991) After the vedas, there is no information on the development of this science in India for a period of about 1,000 years (Anonymous, 1952 & Anonymous, 1986). This was followed by monumental ancient treatise on the subject like Charak Samhita (1,000-800 B.C.), Sushrut Samhita (800-700 B.C.). ( Pal and Jain, 1998) Contribution of the traditional medicine to human health in the 21st century is of paramount importance. Some of the oldest traditional medical systems include Bhutanese (Buddhist), Chinese, Ayurvedic, Unani and Japanese systems of traditional medicine. India has long history of researches on Ayurvedic medicine. Recently, several studies have been conducted on Ayurvedic medicinal plants curing different aliments. (Kirtikar and Basu, 1935) Misra and Kumar (2000, 2001a, 2001b) have worked on crude drugs which have antidepressant properties and also on the medicinally important plants of Rajasthan. They have also worked on the crude drugs used for treating urinary tract stones. Gupta and Kumar (2000a, 2002b), Sanghi and Kumar (2002), Choudhary and Kumar (2001, 2002), Yadav and Kumar (2001) have also conducted studies on Ayurvedic crude drugs for cure of Diabetes, Leprosy, Rheumatism, Digestive diseases and Malaria. Sharma and Kumar (2002) have also worked on herbal cosmetics. With increasing use of traditional medicines globally, attempts are also underway to discover the cure of HIV in the traditional medicine system (Kumar, 2000a). The W.H.O. has estimated that perhaps 80% of earth's 6 billion inhabitants depend upon traditional medicine for their primary health care needs and a major part of this therapy involves the use of plant extracts for their active principles (Farnsworth, 1990). Scientists in many parts of the world have carried out extensive researches and have proved to the humanity the effective use of herbal medicine. The Indian sub-continent is unique in the richness of its plant wealth. Over 15,000 species of higher plants occur in India, of which about 9,000 have multiple economic uses. Of these, 7,500 have medicinal value, 3,900 are edible, 700 are culturally important, 525 are used for fibre, 400 for fodder, 300 for pesticides and insecticides, 300 for gum, resins and dye and 100 provide insence and perfume (Jain, 1968). This floristic diversity is spread over the natural habitats in different vegetation or forest types. It is in the remotely located areas in forests, where the native tribes live. They use the plant wealth of their surroundings and practice traditional agriculture in keeping with their own life styles, rituals and beliefs (Jain, 1991). The climatic regions of India vary from hot dry deserts to the wettest regions on the earth and from tropical to cold alpine regions(Bharucha, 1983). Consequently, the country possesses a vast variety of forest types and arboreal species. (Fig.1.1 and 1.2) as detailed below : 1. Tropical Wet Evergreen forests : These occur in regions with an annual rainfall of 290-320cm, short dry season (of about 3-4 months) and a mean annual temperature of 26-28ºC. These forests extend along the Western Ghats. The flora most widely distributed are Dipterocarpus and Hopea. Other components are Guttiferae Anacardiaceae, Meliaceae. 2. Tropical Semi-Evergreen Forests : These forests occur in regions where there is adequate moisture but not enough for an evergreen vegetation. The average rainfall varies from 2,000-2,500mm and the dry season longer (for 4-6 months). These forests are confined to low hills and undulating ground and may also occur on flat plateau. Flora consists of evergreen as well as deciduous trees. Species of Xylia, Terminalia, Artocarpus, Dalbergia and Sterculia are found here. 3. Tropical Moist Deciduous Forests : These occur in all parts of India with medium rainfall of 10-25cm, and a mean annual temperature of 24-27ºC. The chief feature is a period of leafless existence in the dry season, generally in March and April. Principle species found here are Salmalia malabaricum, Cassia fistula, Erythrina indica, Tectona grandis; various species of Terminalia, Pterocarpus, Xylia and Adina are also present. 4. Littoral And Swamp Forests : These include what are known as beach and dune forests and mangroves. Characteristic of the beach forest are Casuarina, Equisitifolia, Calophyllum inophyllum, Erythrina variegata and Pandanus. The soil is mostly sea sand. 5. Tropical Dry Deciduous Forests : Such forests occur in regions with an average rainfall of 90 to 130cm. and long dry season of 6 months. Tectona grandis, Acacia catechu, Boswellia serrata, Sterculia urens, Tamarindus indica and Shorea robusta are commonly found here. 6. Tropical Thorn Forests : They occur in semi arid regions with short period of annual rainfall ranging from a total of 50-90days in a year. There are open forest of thorny trees. The dominant genus is Acacia. The principle species are A. catechu A. catechuoides. Other thorny species Mimosa, Zizyphus and Euphorbia spp are also found. 7. Tropical Dry Evergreen Forests : Trees are about 9-12m high and form a complete canopy. Shrubs and creepers form the undergrowth. Mean annual temperature is 27-28ºC, dry season varies from 3 to 6 months. The commonest genera are Manilkara (Sapotaceae), Memecylon (Melastomaceae) and Eugenia. 8. Sub-Tropical Pine Forest : Found all along the Himalayan region from north west frontier to extreme north east covering Sikkim and extends further into Assam. Rainfall varies from 150-300cm. Predominant broad leaved trees are Quercus associated with Rhododendrons, Mallotus etc. The pines are Pinus roxburgii, Pinus insularis. 9. Montane Wet Evergreen Forests : Occur in the hills of south India at the height exceeding 1,500m and also in north in the Himalayan regions. Common species found in south are Ternstroemia gymnathera, Eugenia calophyllifolia, E. montana etc. In the north Quercus lamellosa, Q. pachyphylla, Rhododendron arboreum etc are common. 10. Himalayan and Subalpine Forests : In the western and central Himalayas, there are deciduous forests known as Ban Oak forests (Quercus incana) and Moru Oak forests (Quercus dilata). These give place to mixed coniferous forests of Deodar, Spruce, Blue Pine etc at higher altitudes. Gradually, these forests pass into parklands and ultimately into open pastures. Rhododendrons occur at height of 3,500m - 5,000m. 11. Alpine Pastures : They are situated very high at 4,000 to 5,000m. The precipitation here is generally in the form of snow. The alpine meadows, though reckoned among grasslands, have very little grass. The principle vegetation, consisting of perennial mesophytic herbs, Primula, Anemone, Iris and Gentiana, spread their bloom in summer in regions lying just below the snow line.