Growth and Development of the Banana Plant

Abstract

This is a study of the vegetative growth of the banana plant, with special reference to the structure of the shoot apex, the origin of the leaf primordia and buds, and the growth of the leaf base into the pseudostem. The various regions in which intercalary growth contributes to the vegetative plant body are described. The anatomical structures observed are illustrated by photomicrographs. Binucleate cells are conspicuous in the leaf bases and in cells produced by intercalary men-stems. The formation of the air chambers which are characteristic of the mature leaf and of the septa, which are formed as persistent sheets of cells which bound these chambers, is described. The cell divisions which build the septa, and also those which cause the eccentric growth of the midrib are noted, and their proximity to adjacent vascular strands is stressed. Other marginal meristems build the lamina of the leaf. The function of the central apical meristem of the shoot is not to create a massive axis which grows in length, for this vegetative function is taken over by the lateral organs, the growth of which greatly overshadows that in the main axis. However, as the vegetative shoot grows older, its central mass of meristem does become progressively larger. Cell divisions in this central area are sparse, though sufficient to increase its bulk slowly, while the main organ-building and cell-multiplying functions are delegated to the lateral organs. This condition changes on flowering when a massive, true, erect stem forms. Axillary buds do not occur in the vegetative shoot, but adventitious buds appear in an anomalous situation. The vegetative shoot behaves as though there is an extremely strong apical dominance, which suppresses all buds and growth in the axis itself. But an elusive question is the mechanism which stimulates, or controls, the behaviour of so many dividing cells, distributed so widely, through so many discrete areas of cell division or intercalary meristematic activity. The frequent proximity of vascular strands, as probable sources of both nutrients and stimuli to cell division, is suggestive here.