Petri dishes and agar form the foundation of the culture plate technique pioneered by Robert Koch, facilitating the cultivation and study of microorganisms. Agar, derived from red seaweed, solidifies into a transparent medium for microbial growth. Agar plates are classified as nonselective, allowing general growth, and selective, inhibiting specific microbes. Petri dishes, with a dish and lid, provide containers for agar, supporting microbial growth. This technique has revolutionized microbiological research, enabling advances in fields like bacteriology, mycology, infectious diseases, and biotechnology.