Tendrils are thin, long, thread shaped organs that wind tightly around a thin rod, a shoot or the stalk of another plant. The tendrils of different plant groups are not homologous. They can be modified shoots (Vitis), specialized leaves (Pisum), leaflets (Vicia, Lathyrus), leaf stalks (Clematis) or parts of roots that originate directly from the shoot (Vanilla). In the case of Vitis vinifera and Bryonia dioica, the tendrils are lateral shoots usually opposite to a leaf. In Passiflora, the tendrils are modified axillary bud.
So, the correct option is 'Axillary bud'