DIVISION OF STARCH‐CONTAINING CELLS

Abstract

DIVISION OF CERTAIN CELLS whose contents indicate a state of physiological specialization has been reported recently by several investigators. Bloch (1947) noted the retention of the power of multiplication for a considerable time after differentiation by some idioblasts such as oil cells, tannin cells, and cells containing crystals of calcium oxalate. In Ricinus the secretory cells whose contents give the reactions of tannin and fatty acids divide along with the rest of the ground parenchyma cells in the intercalary rib meristem of the internodal regions (Bloch, 1948). Ball (1950) observed that tannincontaining cells as well as clear cells could function as initials of files of cells at the margins of callus cultures of Sequoia sempervirens. The present paper reports observations on division of the starch-containing cortical parenchyma cells of young potato tubers (var. Irish Cobbler). Multiplication of these cells occurs during the normal development of the young tuber. Their division is of interest not only because they are physiologically differentiated cells but also because of the prevalent idea that division of starch-containing cells is preceded or accompanied by digestion of the starch grains. This idea is supported by the observations of some investigators on the development of wound periderm in the potato. Priestley and Woffenden (1923) observed that within a few days of the formation of a suberin or fatty deposit on the cut surface of a potato tuber, the cells just below the surface rapidly lose their starch content and the cork meristem then arises within this region. Steward et al. (1932) found that potato discs respiring in air showed extensive starch disappearance to a depth of 0.8 mm. below the cut surface and the development of a cork cambium in this surface region of starch depletion. Their figure 8A shows that the starch depletion in the surface region was partial rather than complete. One brief reference to the division of potato tuber cells that contain starch grains has been found in the literature. Nemec (1899) noted that the spindle fibers in the vicinity of vacuoles or starch grains adjacent to the nucleus were shorter t-han the other fibers and he figured two large starch grains near a dividing nucleus. Division of cells containing starch would be expected to take place in any developing homogeneous tissue in which starch storage begins before enlargement of that tissue by cell division has ceased. It seems probable, therefore, that division of starch-containing cells is not