Abstract
Certain developmental features of cell wall hydrolysis were studied in the secondary xylem of poplar (Populus italica Moench). At the intervascular pit membrane hydrolysis starts prematurely before differentiation of the secondary wall is complete and increases progressively. Eventually the whole of the middle lamella is hydrolysed, and the primary wall undergoes lytic modification. The modified polysaccharides are dispersed, presumably by the transpiration stream. During differentiation the vessel-parenchyma pit membrane remains unaltered and undergoes thickening. The present investigation suggests that the plasalemma plays an important role in the ordered hydrolysis of certain regions of the primary walls.