The light-induced development of chloroplast membranes has been widely studied and models describing the course of this development have been proposed by various investigators. The development of the chloroplanst in higher plants as described by von Wettstein is briefly reviewed. Revisions of this scheme are suggested, based on more recent data, especially work using improved fixation methods for electron microscopy. Transformation of the prolamellar body takes place via a direct conversion of the prolamellar body into thylakoids, without an intervening stage of vesicle formation. The conversion is through the extension of membranes from the prolamellar body, non through and alignment of discrete vesicles which have broken off from the prolamellar body. The development of the etioplast and formation of the prolamellar body have been shown by recent work to involve growth of continuous membranes which may be attached to the inner membrane of the chloroplast envelope as well as the prolamellar body. Thus, c...