ABSTRACT
In the green leaves of higher plants, the process of photosynthesis occurs within chloroplasts. Under the electron microscope, these organelles have an outer envelope consisting of two membranes. The envelope encloses the stroma of the chloroplast, in which floats a complex internal membrane structure with distinct features: regions of closely-stacked membranes (grana) interconnected by a three-dimensional network of membranes (the stroma thylakoids). The grana were, until recently, regarded as being made up of piles of essentially separate discs (thylakoids) interconnected by stroma thylakoids, but in fact, the network of interconnections is so extensive that the internal spaces of both granal and stromal thylakoids are all effectively in contact with each other.
