MORPHO‐HISTOGENIC STUDIES ON TENDRILS OF VITACEAE

The origin and development of the tendrils were studied in 16 species of the Vitaceae: Ampelopsis (7 sp.), Parthenocissus (4 sp.), Vitis (3 sp.), and Tetrastigma (1 sp.). Two types of arrangement of leaf and tendril occur: (a) two successive nodes have leaf‐opposed tendrils alternating with each other, followed by a third node, with a leaf unopposed by the tendril; (b) all the nodes have leaf‐opposed tendrils. The tendril, like a leaf, is a lateral product of the apical meristem of the shoot. A leaf opposite a tendril is initiated earlier than the tendril. Anticlinal and periclinal divisions in the second and/or third layer of the peripheral meristem of the shoot apex initiate the tendril. The procambium of the tendril first appears towards its abaxial side. Vascularization of the tendril is independent of the axillary bud of the next node below. The positional relationship of the nodal plate vis‐à‐vis the leaf‐opposed tendril shows that the tendril and the leaf belong to the same node. Histological evidence does not show the uplifting of the tendril to the next node above during internodal differentiation. Ontogenetic and morphologic correlation and homology between the inflorescence and the tendril do not substantiate that the tendril in the Vitaceae is an organ sui generis. All available evidence indicates that the tendril is an extra‐axillary lateral branch.