As the natural pattern of development and rubber synthesis in guayule (Parthenium argentatum) is cyclic any treatments to improve growth and rubber production should be synchronized with the normal sequence of events pertaining to growth and metabolism. Starting with 25-week-old seedlings an attempt has been made to acquire information about rubber deposition, growth and defoliation. Observations were made in the field as well as at the light and electron microscope level. Rubber is deposited mainly in the bark during winter. The highest deposits were found in the secondary stem tissue.S. Afr. J. Plant Soil1986, 3: 21–26