Mallow pollen. Coloured scanning electron micrograph (SEM) of mallow (Malva sp.) pollen grains on a pistil. The grains have a spiked outer wall (exine), which may assist in their dispersal by improving their adherence to pollinating insects. Each pollen grain contains a male gamete (reproductive cell) that is intended to fertilise an egg or ovule (female gamete), and initiate the formation of a seed for a new plant. Pistils hold a plant’s female reproductive structures.