LACTUCA SCARIOLA

The genus Lactuca includes dozens and dozens of species. Many of them have the property of orienting their leaves along a north-south axis... In the photo opposite, the needle shows this axis (red indicates North).

LACTUCA, THE COMPASS PLANT.

Lactuca scariola, the wild ancestor of our lettuces, has the particular habit of orienting its leaves along the north-south axis so as to protect them as much as possible from sunburn at the hour when the sun beats down hardest, around midday.

At that hour the leaves present themselves in profile, edge-on, along a north-south axis, avoiding any unnecessary evaporation. The plane of the leaf is perpendicular to the ground. They keep this orientation at all hours of the day.

At that moment, if you draw a vertical line between the sun and the horizon, the point where it meets the horizon shows exactly due south (at least in the Northern Hemisphere). In France, when summer time is in force, you need to add 2 hours: it is noon when your watch says 2 p.m.

LACTUCARIUM, THE SLEEPING DRAUGHT OF ROMAN MOTHERS

Particularly worth noting is Lactuca virosa (wild lettuce), which, when broken, releases a white latex that Roman mothers used to soothe their children or send them to sleep. This dried latex, or lactucarium (and not "lactarium" as one sometimes reads on the internet), does indeed have pronounced sedative properties. The Théralène of Antiquity! Which just goes to show that getting children to fall asleep quickly is not only a concern of today...

Michel