The anatomy of the shoot apex of Rotala rotundifolia (Roxb.) Koehne (Lythraceae)

The structure of the shoot apex of Rotala rotundifolia is described with special attention to the initiation of leaf and axil bud primordia. A comparison is drawn between the vegetative shoot apex in aquatic and terrestrial plants and the apex of the inflorescence. The histogenesis of the apex is consistent with the tunica corpus hypothesis of Schmidt (1924). The zonation in the apex is clearly defined, easy to delineate, and stable. The number of apical initial cells is low. A quiescent zone has not been observed. All types of leaf are initialed in the second layer of the two-layered tunica, very close to the centre of the apex. Corpus cells do not participate in the formation of the leaves. Buds in leaf-axils are formed by derivatives of corpus-cells surrounded by a two-layered tunica. An axial procambial cylinder, provided with a pith, appears above the entry of the youngest leaf-traces. It is concluded that the three types of apex in Rotala rotundifolia (the vegetative apex in terrestrial and submerged plants and the inflorescence apex) are built up in the same manner.