THE ANNUAL CYCLE OF SIZE CHANGES IN THE FUSIFORM CAMBIAL CELLS OF CHAMAECYPARIS AND THUJA

Abstract

In stems exceeding a few inches in diameter most of the pseudotransverse divisions involved in the multiplication of fusiform cambial cells occur toward the end of the growing season. Often these aestival transverse divisions are immediately followed by extensive elongation of the new-formed cambial Cells, especially at their overlapping tips. In the succeeding year relatively slight elongation ensues during the development of the first quarter of the annual ring, but through the succeeding quarters the amount of extension increases and is usually maximal in the final quarter. The actual rates of elongation remain undetermined. The multiplication of fusiform initials is accompanied by loss, most of the failure taking place during the last quarter. Generally the fusiform initials with the most extensive ray contacts survive and enlarge, and those with poor ray associations fail or are reduced to potential ray initials. The elongation and multiplication of fusiform initials tend to produce local ray deficiencies. Reduction of the fusiform initials with the poorest ray contacts to ray initials rectifies to varying extent the ray shortages in those areas.