 and less where light is not falling.
- Do you find any difference in the shape of epidermal cells?
The straight portions of the epidermal cells shows no bending but the bending portions of epidermal cells shows bending.
- Who performed experiments on phototropism?
Charles Darwin and his son Francis Darwin performed some experiments on phototropism.
- What did they do in their experiment?
Charles Darwin and his son Francis Darwin performed experiments on phototropism. They covered the terminal portion of the tip of stem (coleoptile) with a cylinder of metal foil. Exposed the plant to light coming from the side.
- What did they observe by that experiment?
They observed that the bending towards the light (characteristic) of the seedling did not occur. If light was permitted to penetrate the cylinder bending occurred normally.
- What did Charles Darwin and his son Francis Darwin state on their experiment?
They stated that when seedlings are freely exposed to a lateral light some ‘influence’ is transmitted from upper to the lower part causing the material to bend.
- What are the experiments of F.W. Went and how did he succeeded in separating ‘influence’ from the plant?
F.W. Went cut off coleoptile tips from oat seedlings. He placed the tips on a slice of agar and left them for about an hour.
He then cut agar into small blocks and placed a block on one side each stump of the decapitated plants. They were kept in the dark during the entire experiment. Within one hour he observed a distinct bending away from the side on which agar block was placed.
- How did Went come to know about auxin?
Went interpreted these experiments as showing that the coleoptile tip exerted it’s effect by means of chemical stimulus rather than a physical stimulus such as an electrical impulse.
This chemical stimulus came to be known as auxin. In this way the first plant hormone auxin was discovered by F.W. Went.
- What is the meaning of auxin in Greek?
The Greek word auxin means to increase.