Structure of the Vegetative Shoot Apex of Clethra barbinervis

Abstract

The vegetative shoot apex of Clethra barbinervis Sieb. et Zucc. was analyzed inssuperficial and transectional views. There is a central zone the size of which prominently fluctuates during a plastochron, its size becoming maximum in the maximal area phase of the apex, minimum in the minimal. The peripheral meristem, which consists of radially arranged files of cells, is subdivided into five zones associated with leaf primordia. Thus, the area of the apex can be divided into five sectors (sectors 0-4), each of which consists of a leaf primordium and a peripheral zone (“peripheral zone” refers to a portion of the peripheral meristem), except sector 0, in which a leaf primordium has not differentiated yet.The process of growth of a peripheral zone, which is situated between the central zone and a leaf primordium, is very complicated. This process is not simply monotonous increase but is correlated with increase and decrease of the central zone as well as the growth of its subtending leaf primordium and other sectors.