Florigen is produced by:

Explanation

Florigen is a plant hormone produced in the leaves. It acts as a long-distance signaling molecule that travels to the shoot apical meristem, promoting the transition from vegetative growth to flowering. This process is crucial for the plant's reproductive success. Option C is correct because leaves are where this hormone is synthesized. Options A, B, and D are incorrect as flowers, flower-buds, and fruits do not produce florigen. They play roles in the reproductive cycle of plants but are not the source of this specific hormone.