The axillary bud or terminal bud may modify to form tendrils which are specially called stem tendrils. eg: passiflora.

Modified tendrils in Passiflora:
Passiflora, commonly known as passionflowers, have modified tendrils that aid in climbing and supporting the plant. These tendrils play a crucial role in the plant's growth and survival.

Axillary buds:
The tendrils in Passiflora are modified axillary buds that have adapted to become specialized structures for climbing. They emerge from the nodes of the plant and help in securing the plant to a support structure.

Function:
These modified tendrils are essential for Passiflora plants as they enable them to climb and reach sunlight more efficiently. This adaptation allows the plant to access more sunlight for photosynthesis and compete for space in dense vegetation.

Structure:
The tendrils are slender, wiry structures that are sensitive to touch. When they come into contact with a support structure, they coil around it, providing the plant with stability and support as it grows.

Adaptation:
The modification of axillary buds into tendrils in Passiflora is an evolutionary adaptation that has allowed these plants to thrive in various habitats. By utilizing tendrils for climbing, Passiflora can reach greater heights and maximize their exposure to sunlight.
In conclusion, the tendrils in Passiflora are specialized structures that have evolved from axillary buds to aid in climbing and support. These modified tendrils play a vital role in the growth and survival of Passiflora plants in their natural habitats.