The organization of the primary wall in differentiating conifer tracheids

Abstract

In a study of differentiating tracheids of Pinus radiata evidence has been obtained which suggests that, in those cells with localized apical growth, surface enlargement takes place by the multi-net mechanism of wall growth. Features described, such as the difference in microfibril orientation on the inner and outer surfaces of the cell wall and the existence of well-developed corner thickenings, closely resemble similar features in elongating coleoptile parenchyma. It is argued that growth is not limited to the extreme tips of the cells as in root hairs, but that the growth zone extends some distance back from the cell ends.