The Shoot Apex of Some Monocotyledons

The form and structure of the apex of five genera of monocotyledons have been investigated according to methods which have already been applied to other groups. It is found that the growing-point exhibits a cyto-histological zonation: the meristem is organized into four distinct regions, the cells of which differ in appearance and properties and in their direction of division. It is therefore suggested that the tunica-corpus concept is a convenient basis for the description of the apex in this group of plants. Both layers are derived from a small group of apical initial cells which in each species are clearly differentiated from the more active meristematic tissue to which diey give rise. The corpus may be further subdivided into a central region of rib meristem where divisions are predominantly transverse, and a peripheral flank meristem which is actively concerned in leaf initiation. The relationship of the growing-point and youngest leaf primordium is described and problems relating to leaf initiation are briefly discussed.