We examined root development in a variety of cotton and three of its genetically modified derivatives, RR, Bt, and RRBt. The cortex in all was essentially the same; Casparian bands developed in the endodermis at 5-10 mm behind the root tip. There was then rapid development of suberin lamellae opposite the protophloem; passage cells remained opposite protoxylem. Further develpoment resulted in an endodermis with Casparian bands, suberin lamellae, and some secondary wall thickening. The cortex in the genetically modified forms was slightly smaller than the control; none had an exodermis. The stele in the control had fewer cells with lignified walls than the GMO's; secondary growth quickly followed.

Key words: cell wall modifications, cotton, GMO's, root development