The pea plant in the photograph above is one of the many plants that are classified as long-day plants. Scientists and researchers use photoperiodism as a way of classifying most plants. Plants can be classified as long-day plants, short-day plants, or day-neutral plants. The naming system for the plants is rather self-explanatory. Photoperiodism is a series of physiological reactions that organisms undergo in response to the time and length of days. These reactions occur in both plants and animals. In plant, these reactions are defined as developmental reactions in response to the amount of light or dark hours perceived by the plant. Long-day plants are plants in which their hours exceed that plant’s standard critical photoperiod. These plants are usually found in the northern hemisphere during the spring and early summer times. Long-day plants are plants that require a certain amount of daylight in order for the plant to flower. Some examples of long-day plants include wheat, lettuce, and peas.