Pollen grains. Coloured scanning electron micrograph (SEM) of a pollen grain from a marrow plant (Cucurbita sp., left) and a forget-me-not plant (Myosotis sp., lower right). Marrow pollen is amongst the largest of any plant, whilst forget-me-not pollen is amongst the smallest. There is great variation in the size, shape and surface texture of pollen. The outer wall (exine) is highly sculpted in many plants, which may assist in dispersal. Each pollen grain contains a male gamete, which fertilises the eggs or ovules, initiating the formation of plant seeds. Magnification: x363 at 6x7cm size.