It is the ability of some cells to orient themselves or move towards or against a light source. It is similar to phototropism, but are used in different cases. The first is for animal, plant and robotic movements; the second is used almost exclusively for plant growth. It consists of Greek voices 966; 969; 962; ( foos "light" ) 964; 945; 958; 953; 962; ( taxis "order, arrangement, alignment" ). See tactism, thermotactism.
