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Cover  Cortical arrays of microtubules mirror the orientation of cellulose fibers in the walls (cw) of interphase plant cells. This discovery by Ledbetter and Porter (J. Cell Biol. [1963] 19, 239) set the stage for ongoing studies that reveal close associations between the cytoskeleton and the plant extracellular matrix, the cell wall. Because microtubule-destabilizing drugs can cause cellulose fibers to be deposited randomly (for example, see Green, P.B., Science 138, 1404), these cortical microtubules are thought to control the pattern of new cellulose deposition. The placement of new cell walls determines plant morphology, and the orientation of cellulose fibers constrains cell expansion. As cells enter mitosis, a band of cortical microtubules (the preprophase band) predicts the site of the new cell plate that forms between the daughter cells (Pickett-Heaps and Northcote, J. Cell Sci. 1, 121). Thus the cytoskeleton plays a key role in regulating plant development and morphology through the control of new cell wall synthesis. Recently, Cleary and Smith (Plant Cell [1998] 10, 1875) characterized the tangled1 mutant of maize, a defect that disrupts the orientation of leaf cell divisions. In tangled1 mutants, the interphase cortical arrays of microtubules are aberrant and although the preprophase band of microtubules forms, it no longer predicts the site of new wall synthesis. Curiously, the macroscopic structure of tangled leaves is quite normal, despite the defect in cell shape. Alignment of cortical microtubules across the boundaries of the tangled cells raises the possibility that cytoskeletal organization can control the shape of entire tissues and organs. Figures are reproduced from The Journal of Cell Biology, 1963, 19, pp. 243 and 247, by copyright permission of The Rockfeller University Press, and from Introduction to the Fine Structure of the Plant Cell, 1970, p. 44, by copyright permission of Springer-Verlag, New York.Daphne Preuss