Coloured scanning electron micrograph (SEM) of haematopoietic stem cells from the bone marrow at various stages of maturity. These cells form the precursors to every type of blood cell, including white blood cells, red blood cells and platelets. Blood cells are produced constantly by bone marrow as their lifespan is so short. Red blood cells, for example, last on average only 120 days before being broken down. The picture was created as part of a cooperation with Quintessenz Publishing. Magnification: x6,000 when printed at 15cm wide.