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
Cortex (botany) Cortex (botany) A cortex is the outermost layer of a stem or root in a plant. In botany, the cortex is the outermost layer of the stem or root of a plant, bounded on the outside by the epidermis and on the inside by the endodermis. In plants, it is composed mostly of differentiated cells, usually large thin-walled parenchyma cells of the ground tissue system. The outer cortical cells often acquire irregularly thickened cell walls, and are called collenchyma cells. Some of the outer cortical cells may contain chloroplasts. It is responsible for the transportation of materials into the central