Botany, the study of plants, is one of the major fields of biology, together with zoology and microbiology, and has been around for a very long time. Aristotle and Theophrastus, who lived in ancient Greece around the 4 th century BC, were both involved in identifying and describing plants. Theophrastus has been called the 'father of botany' due to his two well-known books on plants that are still influential. The early study of plants, however, was not limited to Western cultures. The Chinese developed the study of botany along lines similar to the ancient Greeks at about the same time. In 60 AD, another Greek, Dioscorides, wrote De Materia Medica, a work that described a thousand medicines, 60 percent of which came from plants. It remained the guidebook on medicines in the Western world for 1,500 years until the compound microscope was invented in the late 16th century. During the 17th century, progress was made in plant experimentation. In the 19th century, rapid advances were made in the study of plant diseases after the potato blight that killed potato crops in Ireland in the 1840s. The study of plants continues today as botanists try to understand the structure, behaviour, and cellular activities of plants in order to develop better crops and create new medicines.