A NEW ASPECT OF CORTICAL DEVELOPMENT IN ROOTS

Heimsch , Charles . (Miami U., Oxford, Ohio.) A new aspect of cortical development in roots. Amer. Jour. Bot. 47(3) : 195—201. Illus. I960.–Excised roots of some tomato varieties exhibit a pronounced increase in diameter of the apex when grown in culture. Anatomical study demonstrated that most diameter growth was attributable to an increase in cell number across the cortex, this having resulted from a progressive increase in the number of periclinal divisions in the innermost cortical cell layer. Although these divisions occur within 200 microns or less of the root apex, their differential distribution during development can be inferred from the cell pattern at mature levels in the basal portion of the tip. Nearly all roots showed an unequal distribution of the last periclinal divisions, there being at some levels more in sectors peripheral to phloem strands than elsewhere. Toward the tip from such levels the sectors of widened cortex were extended around the central cylinder, in some cases around the xylem poles to complete a layer, of newly added cells. The findings are discussed in relation to developmental implications and interpretations and possible causal factors are reviewed.