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Apical Dominance (page 2)

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Author: Janice VanCleave

Design Your Own Experiment

Does the auxin in commercial products such as blossom set actually prevent fruit from prematurely falling from the plant? Is it possible that the plant would produce its own auxin if provided with the proper nutrients? Grow tomato plants in soil with varying amounts of nitrogen and phosphorous. With the assistance of a professional at a nursery, select at least eight dwarf tomato plants that can be grown in large buckets and choose nitrogen- and phosphorous-rich fertilizers and a prepared product designed to set the blossoms on tomato plants. Divide the plants into two groups. At the time suggested on the blossom-set product label, spray half of the plants in each group. Table 17.1 indicates the different nitrogen (N) and phosphorous (P) levels that each plant receives. It is also a sample data table that you can use when recording and displaying your results.

Get the Facts

  1. A chemical growth stimulator called auxin seems to affect fruit development, apical dominance, abscission, positive and negative tropism, and other plant growth. Use biology texts to find out more about the discovery and role of auxin. Describe and even duplicate the experiments of early scientists such as Charles Darwin, Peter Boysen-Jensen, and F. W. Went.
  2. In the fall, leaves from deciduous trees drop off. Auxin plays and important role in abscission. As long as leaves and fruits produce auxin, they remain firmly attached to their stems. Auxin appears to be produced in leaves and fruits, and reduction of the hormone causes abscission. Find out what stimuli trigger the reduction of auxin production. What is the importance of leaf drop? How is it a valuable adaptation for deciduous trees? How do the shape and the texture of nondeciduous plant leaves make annual fall leaf drop unnecessary?
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