A three-dimensional regular lattice found in *etioplasts
. It is composed of a continuous system of tubules but when exposed to light the symmetrical arrangement is rapidly lost as tubules become pinched off into two-dimensional sections of lattice. These form perforated sheets of membrane that move apart, extend and increase, finally establishing the typical granal and intergranal lamellae of the mature *chloroplast
in the etioplasts are dispersed as their lipid contents are utilized in membrane formation.