After the formulation of the photosynthetic unit (PSU) concerning the cooperation of 2400 chlorophyll molecules in the reduction of one molecule of CO2 by Emerson and Arnold in 1932, the search for a morphological expression of the functional unit began. The quantasome hypothesis is an attempt to relate the structure visible in the electron microscope, the quantasome, and the PSU. The term 'quantasome' was introduced by Park and Calvin as a name for grana subunits. The quantasomes were regarded as the main integral parts of the grana lamellae in the protein lipid layers. Yet it soon became clear that a morphological unit such as the quantasomes did not exist. Nevertheless, the term was still used in various applications till the eighties.