How do auxins promote the growth of a tendril around a support?

Q.  How do auxins promote the growth of a tendril around a support?

 

Answer:-

Auxin increase in concentration in the part of the tendril which is away from the support. This results in increased cell division in that part. The part which is nearer to the support has lesser rate of cell division. As a result, the external part of the tendril grows more than the internal part and the tendril coils around the support.