SOME ASPECTS OF THE ELONGATION OF FUSIFORM CAMBIAL CELLS IN THUJA OCCIDENTALS L.

Abstract

An outstanding feature of the elongation of fusiform initials is the high degree of variability that exists from cell to cell. This individual inconstancy is to some extent related to recurrent alterations in the local environment. Thus loss of a neighboring cell often results in accelerated elongation. Although frequently masked by the deviations in individual cells, certain general trends of growth become apparent on analysts of the data from numerous cells. In the growth cycle between successive multiplicative divisions the progress of elongation is not uniform but rather follows a familiar growth pattern, early rapid extension giving way to a gradually decreasing rate of elongation as lengthening proceeds. Growth at opposite ends of the same cell is usually dissimilar, basipetal extension tending to predominate. This bipolar difference is evident in the stems of small trees, in the periphery of the stems of mature trees, in the distal parts of branches, and to a lesser degree, in the proximal parts of recurved branches. The reduced bipolar difference in the inverted proximal portions of recurved branches indicates that gravity is not the major factor in the establishment of polarity, but does perhaps play a minor role. Cell elongation is apparently achieved by tip growth.