Pollen tube through wind, water or pollinators. The last step before fertilization is the growth of the pollen tube to transfer non-motile sperm to the protected egg. Pollen tubes are unique to plants and their structure had evolved over plant history. The pollen tube formation is complex and the mechanism is not fully understood, but is of great interest to scientists. Pollen is produced by the stamen, the male reproductive organ of the flower. Each pollen grain contains a vegetative cell, and a generative cell that divides to form two sperm cells. The pollen is delivered by the opening of anthers for
Flower constancy for certain flower types and constantly return even if other more rewarding flowers are available. This is shown for example in experiments where honeybees remain flower constant and do not attempt to feed on other available flowers that exhibit an alternative color to their preferred flower type. Flower constancy favors flower pollination, that is, pollinators that are flower constant are more likely to transfer pollen to other conspecific plants. Also, flower constancy prevents the loss of pollen during interspecific flights and pollinators from clogging stigmas with pollen of other flower species. Flower constancy can be enhanced when the flowers are