Pollen tube Pollen tube A pollen tube is a tubular structure produced by the male gametophyte of seed plants when it germinates. It acts as a conduit to transport the male gamete cells from the pollen grain—either from the stigma (in flowering plants) to the ovules at the base of the pistil or directly through ovule tissue in some gymnosperms. In maize, this single cell can grow longer than to traverse the length of the pistil. Pollen tubes were first discovered by Giovanni Battista Amici. They are used as a model for understanding plant cell behavior. Research is ongoing to comprehend how
Beta decay atoms obtain a more stable ratio of protons to neutrons. The probability of a nuclide decaying due to beta and other forms of decay is determined by its nuclear binding energy. The binding energies of all existing nuclides form what is called the nuclear band or valley of stability. For either electron or positron emission to be energetically possible, the energy release (see below) or Q value must be positive. Beta decay is a consequence of the weak force, which is characterized by relatively lengthy decay times. Nucleons are composed of up quarks and down quarks, and the weak force