The axillary buds of Bougainvillea are modified into thorns. They serve as a defence mechanism to avoid browsing by herbivores. The axillary buds of Cucurbita are modified into tendrils. They function as a means of support for the plant, allowing it to climb and cling to other surfaces for support. They also serve to display foliage to get proper amount of sunlight to perform photosynthesis and they help in proper display of its flowers to promote pollination.
This is an example of divergent evolution, in which similar structures adapt to perform different functions. Such organs that have similar structure and evolutionary origin but may have different functions are termed homologous organs.