The stimulus in the process of thigmotropism is:

The growth of a pollen tube towards the ovule caused by a sugary substance as stimulus is an example of:

The bending of the shoot of a plant in response to light is called:

A growing seedling is kept in a dark room. A burning candle is placed near it for a few days. The top part of seedling bends towards the burning candle. This is an example of:

Which of the following acts as a stimulus in the process of hydrotropism?