Light micrograph of a transverse section of the Royal fern, Osmunda, photographed through a Leeuwenhoek single-lensed microscope. The picture is a demonstration of what Antoni van Leeuwenhoek (1632-1723), the great Dutch pioneer of microscopy, would have been seen through his simple microscopes in the late 17th century. Magnification: x250 at 35mm size.