cytotaxis

from The Century Dictionary.

• noun The movement of cells, or of cell-masses, in relation to one another. The approach of cells to one another is spoken of as positive cytotaxis, their withdrawal from one another as negative cytotaxis.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Biology) The movement of cells toward or away from other cells, as a result of some stimulation, such as chemical signals transmitted and received by the cells.