Origin and Anatomy of Tubers of Dioscorea floribunda and D. spiculiflora

Abstract

1. The tubers of Dioscorea floribunda Mart. & Gal. and D. spiculiflora Hemsl. arise from a ventral bulge between the first shoot and true root of the seedling. This bulge results from meristematic activity of the ground meristem.2. Primary growth of the tuber is by multiplication and thickening of the primary thickening meristem and by differentiation of the cells so produced. 3. The tissues of the tuber arising directly from the ground meristem are the storage parenchyma, its enclosed bundles of xylem and phloem, a parenchymatous cortex containing a well-defined cambium-like layer, and storied cork. A true periderm exists transitorily. 4. The tuber has a dorsiventral orientation. The dorsal surface gives rise to new aerial shoots, whereas the ventral produces new adventitious roots. Growth of the tuber is more pronounced on the dorsal than on the ventral side, especially in D. floribunda. 5. The anatomy of the tuber is more closely related to that of the stem than to that of the root. 6. The starch supply of the tuber is concentrated in the older tissue. It therefore tends to occur in greatest quantity in the ventral portions. 7. It is concluded that the tubers in these species represent much modified stem tissue, thus being a relic of the ancestral rhizome.