Fig. 6.

Three-dimensional chloroplasts models of the 1960s that replaced those proposed in the 1950s (Fig. 5). a The characteristic feature of the Weier et al. (1963) model is the much exaggerated tubularity of the stroma thylakoids. b The 1963 model shows a planar stroma thylakoid intercepting a cylindrical grana stack. The two images illustrate the front and back sides of the model and the series of connections that connect the stroma thylakoid with the grana thylakoids. In this model, the partial helices formed by the stroma thylakoid are of opposite handedness on the near vs. far sides of a granum. c In the Wehrmeyer (1964) model the stroma thylakoid is depicted as a right-handed helix that spirals around the granum, while also suggesting a mechanism for spiral growth