Read the passage.
The difference between day length and night length is an important environmental stimulus for many plants. This stimulus can cause plants to begin reproducing. Some plants flower only in late summer or early autumn, when the night length is long. These plants are called short-day plants. Examples of short-day plants include poinsettias, ragweed, and chrysanthemums. Other plants flower in spring or early summer, when night length is short. These plants are called long-day plants. Clover, spinach, and lettuce are examples of long-day plants.
Short-day plants flower in the summer or early autumn. Long-day plants: