The Problem of Sampling in Studies of Tracheid Length in Conifers

Location in the tree and rate of radial growth are important factors influencing length of wood cells. Frequency of anticlinal division involved in cambial cell multiplication is a part of the mechanism controlling cell size. Although certain general relationships obtain between these interacting elements, broad fluctuations occur, both within and between trees necessitating recourse to extensive material in studies of cell length. Some guidelines for sampling are proposed. Determination of cell length should be made one-fourth to one-third outward in the annual ring, at which stage of ring development anticlinal divisions are at minimal frequency. Sampling from successive rings is recommended because of ring-to-ring irregularities which are sometimes related to local inconstancies in rate of anticlinal division. Likewise the taking of data from more than two points around the circumference serves to smooth out sectorial differences which may be of considerable magnitude. In tree-to-tree comparisons workers should select trees of similar size and age to minimize differences due to growth rate and stage of tree development.