Multi-celled fibers of cultured ovules of Gossypium hirsutum, cultivar, MD51 ne were used to test the hypothesis that fiber growth occurs exclusively at the tip. Each cell of multi-celled fibers has a nucleus and the number of cells per fiber range from 2 to more than 8. The data, given as regression curves, express the relative length of the tip cell of a given fiber as a function of total fiber cell length. The expected result, if the hypothesis were correct, would be regression curves with positive slopes. The results show, however, that growth of 2- and 3-celled fibers is random producing regression curves with slopes of zero. Fibers with 4 or more cells, on the other hand, have tips cells that grow more slowly than the other cells of the fiber. The regression curve, in this case, has a slight but significant negative slope. Finally, neither IAA nor GA₃ (final concentration 2 mM each), given separately or together, alters the growth pattern of 2- or 3-celled fibers.

These results do not support the hypothesis that fiber cells grow mostly at the tip. They show that the growth of multi-celled fibers occurs randomly along their linear axis.

Research supported by Cotton Incorporated, Department of Energy, Office of Health and Environmental Research, and in part by the Nuclear Regulatory Commission's Historically Black Colleges and Universities Facility Research Participation Program.