solve the CHAPTER MYSTERY

THE GREEN LEMONS

To solve the mystery of why the lemons remained unripe, growers remembered a story from the nineteenth century. In those days, gas streetlights were commonly used in large cities. A few years after such streetlights were installed, city dwellers noticed that trees growing near the streetlamps had developed short, thick stems, and dropped their leaves much earlier than they should have. It was as if hormone levels in the trees had been affected. And, in fact, the levels had changed. One of the components of the gas used in the lights was ethylene.

Recall from Lesson 24.3 that one effect of ethylene is to stimulate the ripening of fruit. Whether the ethylene is manufactured by the plant or externally, as in the case of a kerosene heater, doesn't matter. Because ethylene is a gas, it can diffuse through the air, cell walls, and membranes of a plant and its fruit. When that source of ethylene was taken away from the picked lemons (when the electric heaters replaced the kerosene ones)—the ripening stimulus was removed, and the lemons stayed green.

1. Relate Cause and Effect Tomatoes put in a paper bag with apples ripen much more quickly than those placed in the open air. What would this suggest about the effects of ripe apples on unripe tomatoes?

2. Propose a Solution How could farmers, shippers, and produce marketers use the effects of ethylene to their advantage?

3. Connect to the Recent studies have shown that gaseous hormones are involved in a plant's systemwide response to an attack by herbivores such as caterpillars. What might be the benefits of a gaseous hormone in such a situation?