Essentially, lanes on the secondary cell wall are built with microtubules. Separate sets of "CesA" genes are involved in primary and secondary cell wall biosynthesis. Both non-rechargeable primary cell and rechargeable secondary cell chemistries have been investigated. However, another mechanism is used in secondary cell walls leading to its organization. The secondary cell wall increases their rigidity and tensile strength. The secondary cell then undergoes mitosis to produce more secondary cells. Within a secondary cell, there is a nucleus and between 1 and 6 spores. Wood consists mostly of secondary cell wall, and holds the plant up against gravity. Some secondary cell walls store nutrients, such as those in the cotyledons and the endosperm. Tracheids have thick secondary cell walls and are tapered at the ends. Both cell types have a secondary cell wall and are therefore dead at maturity. The secondary cell wall has different ratios of constituents compared to the primary wall. A silver zinc battery is a secondary cell that utilizes Silver(I,III) oxide and Zinc. The secondary cell wall consists primarily of cellulose, along with other polysaccharides, lignin, and glycoprotein.