The architecture of the extending cell walls of cotton hairs, Juncus stellate pith cells, and maize root hairs has been studied. The observed facts could be explained on the basis of the multi-net-growth hypothesis. The cells investigated were found to be completely enveloped by a continuous network of cellulose fibrils. Every area of the growing part of the cell wall is extending in one or in all directions. The cellulose fibrils in the cell wall must slip past one another. The cell wall does not grow thinner since new fibrils are continuously deposited onto its inner face. In the apex of the root hair, extension is the same in every direction, so that the orientation of the fibrils does not change. In cotton hairs (the extreme tip excepted) and Juncus stellate cell arms, however, a change in fibril orientation has been observed. Here axial extension prevails over transverse. This results in the orientation of the fibrils altering from the moment they are deposited until the area gets out of the growth zone.