Structure of the Angiosperm Apex

Abstract

DURING the past twenty years or so, a considerable amount of research has been carried out, especially in the United States, into the anatomical structure of the vegetative apices of angiosperms. Many of these apices were described in terms of Schmidt's well-known tunica-corpus concept. This concept implied that the apex consists of two zones—the tunica, consisting of one or more layers of cells, where divisions are ordinarily anticlinal, and the corpus, where cell divisions take place in a number of planes. In practice, the application of this concept is an extremely arbitrary procedure. In later years, a number of workers have described zones in the vegetative apex which are distinguished, not by direction of cell division, but by cell size, frequency of cell division and density of cell contents. These workers have distinguished three main zones: (1) the central initiation zone, consisting of comparatively large, lightly staining cells which show few divisions; (2) the flank meristem, consisting of smaller, more deeply staining cells, which show frequent divisions; and (3) the rib or file meristem, where the cells are to be found in well-marked vertical rows.