Isolated chloroplast membranes of the unicellular photosynthetic alga Chlamydomonas reinhardtii were cryofixed, freeze-fractured, and surface replicas observed by transmission electron microscopy. This close-up of wildtype thylakoids shows the transition between the larger particles seen on the 'C' face of unstacked regions of thylakoids (Cu) and smaller particles on the stacked (Cs) face (region at right). See Fig 4 in Goodenough and Staehelin 1971 J Cell Biol 48:595-619.