Abstract It is suggested, that in the formation of coniferous tracheids, the amount of cell-wall material that can be developed in the maturation of a specific cell is a function of the parentage of the cell and is fixed for that cell at the time of cell division. It is further suggested thatquantity of cell wall is essentially the same for all daughter cells originating from a particular cambial initial within an annual ring. Data obtained from a microscopic examination of the xylem of Abies grandis (Dougl.) Lindl. supported this hypothesis. Similar results were observed with Pinus contorta Dougl.