This picture is of lettuce. Lettuce is a long day plant. A long day plant is a plant that flowers when the amount of daylight increases. These plants flower in early summer or late spring. In the 1940’s, scientists discovered that the time that these plants flower has less to do with the amount of daylight they get but rather the amount of darkness they get. The long day plants aren’t long day plants but are more of short night plants. Although the species in the long day plant category may not flower when there is a lot of darkness, the specific amount of hours that each plant needs of darkness varies with each species of plant.