Marigold petal and pistil. Coloured Scanning Electron Micrograph (SEM) of the flower of the common marigold, Calendula officinalis. A petal of the plant (orange) is seen with a pistil (yellow) in front. Petals are modified leaves which attract insects while pistils contain the female reproductive parts of the plant. Calendula officinalis flowers are commonly used as a herbal remedy. The flower heads can be used to make oils, ointments and creams. These are used externally to treat symptoms varying from wounds to headaches. Magnification: x26 at 6x7cm size.