Jean-Jacques d’Ortous de Mairan

Today is the birthday of Jean-Jacques d'Ortous de Mairan, who was born on this day in 1678.   Mairan was a French chronobiologist - a job one rarely hears about these days.
In 1729, da Mairan put together an experiment showing the existence of a circadian rhythm in plants.
Essentially, he took a mimosa pudica plant - the heliotrope - and he put it in constant darkness in a cupboard. All the while, he recorded the plant's behavior. And what do you know? The plant had a natural rhythm of opening and closing its leaves - even if it couldn't absorb sunlight. Now, de Mairan didn't think that the plant had an internal clock, but he DID think that it could attune itself to the sun - even if it was blocked from it.
No matter the accuracy of Mairan's conclusions, his work was on to something, and it established the foundation for chronobiology or the internal circadian clock.