Pollen tube subsequent pollination (transfer of pollen grains to the pistil, the female reproductive organ). Transfer of pollen is usually carried out by wind, water, or animals . The ovaries hold the ovules that produce the female gamete: the egg cell, which waits in place for fertilization. Once a pollen grain settles on a compatible pistil, it may germinate in response to a sugary fluid secreted by the mature stigma. Lipids at the surface of the stigma may also stimulate pollen tube growth for compatible pollen. Plants that are self-sterile often inhibit the pollen grains from their own flowers from growing pollen
Medullary ray (botany) also known as vascular rays or pith rays. In this context, the term refers to radial sheets or ribbons extending vertically through the tree across and perpendicular to the growth rings. Also called pith rays or wood rays, these formations of primarily parenchyma cells allow the radial transport of sap and are essential in the process of tylosis. In quartersawn material, where the wood is cut into boards with the growth rings roughly perpendicular to the face of the board, the medullary rays often produce beautiful figure such as silver grain, medullary spots, pith flecks, etc. Medullary ray (botany) Medullary