The mature vesicles do not possess a boundary membrane. Each vesicle consists of many small droplets, in the range of 50-100 nm in diameter. The vesicles grow by the addition of terpenoids synthesized by ER in the vicinity of the terpenoid vesicles. As the vesicles develop the vacuole fragments into two or more bodies. Plastids, mitochondria and microbodies, and a few dictyosomes also occur.
Lipid bodies accumulate at later stages of development.
The plastids are likely to provide the isoprenoids that may be further elaborated by other organelles. In addition, the vacuoles, cytoplasm and ER may all provide the enzymes and compartments necessary for the synthesis of a large variety of terpenoids. In vitro extraction of terpenoids is possible only if the cultured neem tissues are induced to differentiate secretory cells.