Light micrograph of onion (Allium cepa) meristematic cells, each with two nuclei, during mitosis (nuclear division). Mitosis is the formation of two daughter nuclei from one parent nucleus. At top the nuclei are in metaphase, with the chromosomes aligned in a row. The chromosomes start to move to opposite poles, guided by microtubules, during anaphase (upper centre). At bottom, the cell is in telophase. The separated chromosomes have moved to opposite sides and four new nuclei form around them. Orcein staining.