Cell Displacement Through the Columella of the Root Cap of Zea mays L

Exposing roots of Zea mays to a solution of caffeine for 1 h induces a small population of binucleate cells in the meristem. The progress of the binucleate cell population was then followed, in time, as it was displaced along the length of the cap columella. Since this method of marking cells seems to have no effect on the subsequent pattern of cell proliferation in the cap meristem, the movement of the binucleate cells through the cap is inferred to be similar to the movement of cells in an undisturbed cap. The binculeate cells that persist in the cap are believed to be cells that were engaged in their final mitosis at the time of the caffeine treatment, so the time that it takes for them to appear at the edge of the cap is a measure of the period for which a cell is contained in the non–dividing portion of the tissue before being lost from the cap surface. In roots of Zea grown at 22 °C cells take about 7 days to reach the tip of the cap columella and about 2 to 3 days to reach the flanks of the cap following their displacement from the cap meristem.