The modifications of the plastid structures in a Maize mutant, « golden-leaf », have been studied in the electron microscope. In this mutant plastid organization is temperature dependent. At 25°C the chloroplasts are quite regularly structured, but when the corn plants are transferred to 16°C, the plastids become incompletely organized or anomalous. If higher temperature conditions are re-established, the plastids are able to regain their original organization only if a prolamellar body or structured grana, even in an anomalous state, are present. When the plastids are affected by the lower temperature in a very young stage, their modifications become irreversible, and their appearance resembles, also in the regreened tissues, that of albino plastids or of chromoplasts.