Effective pollination occurs when viable pollen is transferred to a plant’s stigmas, ovule-bearing organs, or ovules (seed precursors). Without pollination, no fertilization would occur. Since plants are immobile organisms, they usually need external agents to transport their pollen from where it is produced in the plant to where fertilization can occur. This situation produces cross-pollination, wherein one plant’s pollen is moved by an agent to another plant’s stigma. Some plants are able to self-pollinate—transfer their own pollen to their own stigmas. But of the two methods, cross-pollination seems more advantageous, for it allows new genetic material to be introduced.