The pollen tubes as a rule emerge at the germ pores on the pollen grains. Almost the entire contents of the grain move into the tube. Rapid growth of the tube is restricted to the tip region. In a growing tube most of the cytoplasm is confined to the apical region, and a lag vacuole fills the grain and the older region of the tube. To restrict the cytoplasm to the apical region of the growing tube, a series of callose plugs are formed at a regular distance behind the tip. As a result a fully grown pollen tube is subdivided into many compartments due to these plugs. The plugs originate as a ring on the inner side of the wall. They gradually grow toward the centre reducing the lumen and, finally, sealing the tube. The small amount of cytoplasm that is left behind the plug on the side of the grain gradually degenerates. The partition in the pollen tube prevents the back flow of cytoplasm and nuclei. The cytoplasm behind the cap block is rich in the usual cell organelles, namely, mitochondria, Golgi bodies, rough and smooth endoplasmic reticulum, vesicles, amyloplasts and lipid bodies.