Water is an essential ingredient of bacterial growth as shown by cultural studies in liquid media, and on cotton in solution, and cotton maintained at various relative humidities. Studies involve microorganisms found on cotton from various areas of growth, and on autoclaved cottons inoculated with organisms isolated from cotton. These laboratory studies assist in the interpretation of studies involving spraying of field cotton. The water (rain, dew, or spraying) is a major determinant of the growth of microorganisms on field cotton. The characteristics of some of the organisms permit their survival for long periods on the cotton.