Fertilization of flowers by pollen is achieved because the ovary releases chemicals that produce a positive chemo-tropic response from the developing pollen tube. This movement of the pollen tube in response to the chemicals is called chemotropism. The pollen tube is made up of two laters. Pollen tubes show many movements apart from growth. Cytoplasmic streaming occurs in all plant and animal cells and it is the intracellular movement of cytoplasm to transport nutrients within the cell.