A plant scientist was hired by a greenhouse operator to devise a way to force iris plants to bloom in the short days of winter. Iris normally blooms as a long-day (short-night) plant. Which of the following has the best chance of creating iris blooms in winter?

(a) Interrupt the long winter nights with a brief period of light. (b) Increase the temperature to more closely follow summer temperatures. (c) Artificially increase the period of darkness in the greenhouse. (d) Grow the plant in 24 hours of light each day.

(a) Interrupt the long winter nights with a brief period of light.

Explanation:

Since Iris plant is a long-day short-night plant and winter is characterized by short-day long-night, the best strategy to employ by the plant scientist is to find a way to interrupt the long winter night with a brief period if light.

In order for iris to bloom, the short-day that comes with winter needs to be extended artificially. This extension can be achieved in a controlled environment like the greenhouse by artificially exposing the iris plant to light during parts of the dark period of the winter.

Option b is incorrect because blooming of iris is correlated to amount of light, not temperature as shown in the illustration.

Option c is incorrect because increasing the period of darkness is inimical to the blooming of iris which requires a long-day in order to bloom.

Option d is incorrect because exposing the plant to 24 hours light will completely remove the short-dark period needed for the blooming.

The correct option is a.