researchers for a hundred years. Cellulose, a primary component of cell walls, was known to be constructed from cellulose granules. These granules had appeared to microscopists prior to this time to emerge fully formed in the cell's protoplasm. By contrast, the formation of starch, which is composed of the same elements carbon, hydrogen, and oxygen, could be seen to occur in stages, in structures called plasmids inside the cell protoplasm. Farr discovered that cellulose-manufacturing plastids do exist in the protoplasm of the cell, but that such plastids had been invisible because they have a light refractive index similar to that of the protoplasm in which they are located. She made the plastids visible in cotton cells by mounting the cells in a new bath derived from the juices of the cotton plant rather than in water, which had been used previously. Notes References Yost, Edna (1943). American Women of Science. Frederick A. Stokes Company, Philadelphia and New York. Plant physiologists 1895 births 1983 deaths American women botanists Fellows of the American Association for the Advancement of Science Fellows of the Royal Microscopical Society Kansas State University faculty Texas A&M University faculty Washington University in St. Louis faculty Columbia Graduate School of Arts and Sciences alumni Ohio University alumni People from Washington County, Ohio 20th-century American botanists 20th-century American women scientists Beltsville Agricultural Research Center scientists