The tendrils that allow pea plants to climb up on an object are modified leaves, whereas the tendrils of grape vines are modified stems explain

Tendrils refer to modifies leaves, petioles or stems with thread like structure which climbing plants used for attachment and support. Depending on the type of crop in question, leaves, petioles or stems can be modified to form tendrils for climbing plants. In case of pea plants, modified leaves are used to form the tendrils while in the case of grapes, stems are modified to form the tendrils.