Florigen is a hypothetical stimulus that controls when a plant will flower in response to the changes in day length associated with the different seasons. Flowering occurs when shoot apical meristems—small regions of prolific cell division in the buds of the main shoot and lateral branches—stop producing vegetative tissues (stems and leaves) and instead produce floral tissues (a process called evocation). The transition to flowering is fundamental to the production of offspring and the survival of the species, and must be coordinated with seasonal change to (1) synchronise flowering within the species to promote cross-pollination, (2) harmonise flowering with the life cycles and behaviours of pollinators such as insects, and (3) coordinate flowering with the seasons to ensure that progeny (seeds) are sufficiently mature to survive unfavourable conditions, such as winter or hot, dry summers. The timing of this transition is also a concern for agriculture since seeds and fruits must be harvested within the growing season of the region.