This form of photophosphorylation occurs on the stroma lamella or fret channels. The upper surface, or "superior" lamella, has transverse and longitudinal ridges and ribs. There are a number of proprietary lamella clarifier designs. A further advantage of the lamella clarifier is its distinct absence of mechanical, moving parts. Therefore, where site footprint constraints are of concern a lamella clarifier system is preferred. The two groups are divided by the basal lamella. For example, pectinase which digests middle lamella among plant cells. The lumen or surface of the lamella has a complex structure. Specifically, pectin in the middle lamella holds neighboring cells together. Calcium is needed to form the pectin in the middle lamella of newly formed cells. The lumen or surface of the lamella, has a complex structure. The lumen, or surface of the lamella, has a complex structure. Doctor blades are traditionally designed in 3 main tip configurations&colon; straight, bevel and lamella. Within the ground scales are layers of lamella. The clitoral hood is formed during the fetal stage by the cellular lamella.