M.I. WALKER / SCIENCE PHOTO LIBRARY M.I. WALKER / SCIENCE PHOTO LIBRARY
Plant cell mitosis. Light micrograph of root tip cells of the onion (Allium sp.), showing mitosis. Mitosis is the usual process by which cells divide. Resting nuclei are seen as the round homogenous dark patches. Before the cell divides, the chromosomes start to appear as long thread- like structures. Each chromosome consists of two identical sister chromatids. These sister chroma- tids then separate, moving to opposite ends of the cell (as at centre). Nuclear membranes then form around the two daughter nuclei and the cell divides. Magnification x200 at 35mm size.
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