Plants 9 - Plants 9 Growth and development: began in plants...

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Plants 9 Growth and development: began in plants in the 1850’s by Sachs. He believed that plants had organ forming substances which determined whether a leaf/flower/stem/root would be produced. Charles Darwin and his son were interested in tropisms, or movements of plants. They were interested in the movement of plants with respect to light=phototropism. They used grass seedlings. Suppose a grass seedling has just germinated. Grass is a monocot. When they germinate, the structure that comes up from the ground is the coleoptiles. They wanted to know the phototropic response of the coleoptiles. Their first experiment was done in total darkness. In total darkness, the coleoptiles grew straight. If they took a grown coleoptiles and gave it light from one direction , or unilateral illumination and waited for some time, the coleoptiles bent to the light. When this coleoptiles bends towards the light, the side on the back of the coleoptiles which is away from the light has to grow more than the side closest to the light. This is called differential growth. What part of the coleoptiles is sensitive to the light? They covered various parts of the coleoptiles. The tip of the coleoptiles perceives the light. Darwin hypothesized that there must be something going on in the tip. In 1897 they published the results in “The Power of Movement in Plants.” In 1930, people began doing experiments on phototropism again. The first they did was they took a coleoptiles and put a piece of aluminum foil between the tip and region that would bend. They gave it light. There was no bending. This agreed that there was something in the tip. They then took a coleoptiles in darkness and put a block on top of the coleoptiles symmetrically. After some time, the coleoptiles elongated but it was straight. In the next experiment, still in the dark, they placed the block asymmetrically. After some time, they found that the coleoptile tip bent in the darkness. The side that elongated was the side nearest to the block. Next they did the experiment in light. They placed the block on top of the
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Plants 9 - Plants 9 Growth and development: began in plants...

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