The case for multinet growth in growing walls of plant cells.

The basis of multinet gwoth, the multinet growth hypothesis, is examined in view of recent criticisms. It is shown that the strain across a growing wall may be calculated by simple means and the expected reorientations are deduced (a) for a wall in which the microfibrils of the innermost wall lamella always lie helically with the same pitch and (b) in which the microfibrils lie at random. Calculations are presented both for cells increasing in length only and for cells also increasing in breadth. Both the strains and the reorientations are smaller than commonly implied and are too small to be reliably detectable in wall sections. Observations on wall sections cannot therefore be accepted as proof that microfibril reorientation has not occured and it is concluded that the multinet growth hypothesis still stands as applying both to parenchyma and to collenchyma cells. In view of the wide dispersity in the structure of the walls of growing cells, it is recommended that the qualifying ‘multinet’ should be dropped and replaced by ‘passive reorientation’.