A researcher discovers that cocklebur will not flower if a required dark long period is interrupted by a brief flash of white light. Which of the following conclusions can be made?
A) A cocklebur is a long-day plant.
B) When the night is longer than a critical length, the cocklebur will flower.
C) The length of the light period controls flowering.
D) Interrupting the light period with darkness will prevent flowering.
Answer: C) The length of the light period controls flowering.