Bone marrow is the spongy tissue at the center of large bones responsible for the production of all the various types of blood cells. This includes red blood cells, platelets, and the various kinds of white blood cells.
According to Science Daily, marrow comes in two types, red marrow and yellow marrow. Red blood cells (for transporting oxygen), platelets (which act as clotting factors to stop bleeding) and most white cells (which fight infection) are produced by red marrow, while yellow marrow produces other types of white blood cells. Marrow is networked with blood vessels and high in fat content.