Do microtubules orient plant cell wall microfibrils?

Cortical microtubules (MTs) allegedly orient nascent cellulose microfibrils (CMFs) in plant cells. The frequently observed parallelism between them, and the effect of MT‐depolymerizing agents, are the bases for this hypothesis. Data have, however, accumulated about cells in which MTs and CMFs are not in parallel alignment. These data will be reviewed. MT orientation cannot be the only factor determining CMF orientation, but MTs could overrule other factors in cells where, for instance, they are more tightly attached to the plasma membrane than in other cells. MT and CMF orientations could, however, both be controlled by a third factor, and CMFs may even impose orientation on MTs.