Name the blood cells, whose reduction in number can cause clotting...

Platelets are formed from the megakaryocytes (special cells in the bone marrow). They play an important role in blood clotting. Platelets can release a variety of substances called platelet factors (e.g. thromboplastin) most of which are involved in the coagulation of blood. They constitute most of the mass of the clot and activate the clotting factors in plasma that results in the formation of fibrin (clot). A reduction in the number of platelets (thrombocytopenia) can lead to clotting disorders which results in excessive loss of blood from the body.