Some central developmental stages of the chloroplasts of Anthoceros have been examined, with special reference to clarification of descriptive concepts applicable to the lamellations. The double membranes (here referred to as doublets) which increase in numbers as simple lamellations become converted into stacks are shown to be folds of a single membrane which grow intrusively into previously formed membrane-bounded slits. These cavities or slits (here termed clefts) also arise as folds of the same single membrane and they alone possess the power to transect the plastid stroma directly. Where clefts meet, their membranes coalesce to produce the meshwork of interconnected clefts into which the doublets penetrate; whether fusions can also occur where advancing doublets reach the end of the space available has not yet been ascertained. The concept of disks, previously current for describing some adult plastids, is discussed and shown to be incompatible with the developmental findings for this organism. The whole structure in Anthoceros is interpreted as the result of growth and folding of one membrane which is ultimately derived from imaginations protruded into the stroma from the innermost layer of the plastid wall. This interpretation brings the chloroplast into line with recent conclusions for mitochondria and vacuoles in the same material.