Describe an experiment showing that shoots are positively phototropic
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An experiment showing that shoots are positively phototropic
1. Remove the glumes of about 30 oat grains and soak the oat grains in water for an hour
2. Fill a plastic cup to the rim with moist vermiculite.
3. Transfer all the soaked oat grains to the cup and place it in a darkroomor a lightproof cabinet until the coleoptiles have reached a height of about 2 cm. This would take 3 to 5 days depending on the temperature. Water whenever necessary
4. Prepare a cardboard box to be used for the unilateral light treatment experiment. The box should be large enough to house the cup with the coleoptiles in their final size.
5. Paint the inside of the box with matt black paint. On one side of the box, cut a horizontal slit about 10 cm long and 0.5 cm wide and at a height that will allow light to enter and strike the coleoptiles when the cup is in place inside the box
6. Place the cup under dim red light (safety lamp) in a dark room. Select oat coleoptiles that are straight and remove any atypical ones by cutting them off with a razor blade at the vermiculite level.
7. Wrap a small piece of aluminium foil (about 8 mm2 ) around the end of a matchstick to form a small hood.
8. Select two adjacent coleoptiles that are about the same height. Detach the hood and place it over the tip of one coleoptile thus shielding the apical 5 mm or so. Leave the other coleoptile unshielded, as the control.
9. Repeat step (7) & (8) four more times resulting in five apically shielded and five control coleoptiles.
10. Place the cup inside the cardboard box. Switch off the dim red light and allow light from a 25-watt fluorescent lamp at a distance of about 50 cm to enter through the slit and strike on one side of the coleoptiles for three minutes.
11. Keep the whole set up in the dark for another 90 minutes.
12. Take the cup out of the cardboard box and observe the orientation of the coleoptiles with respect to the direction of the unilateral light.
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