The summer I was fifteen, I spent a month as an exchange student in a small city in Brittany. The city was called Lannion, and it was adjacent to Perros-Guirec, which was the hometown of my middle school French teacher. Each summer he took a handful of his students back to his birthplace. In retrospect, now that I have a child and live a few thousand miles away from my parents, I imagine he must have started organizing the homestays in order to help him afford to bring his kids back home.

I grew up in south-central Texas, where summers last a long time, and they're hot: really hot. (I couldn't quite fathom it when I was instructed to pack some things with long sleeves.) The beaches I knew were those at Port Aransas and South Padre Island, on the Gulf coast, where the water is warm. And the flora I knew was the stuff that grows at the intersection of subtropical and scrub desert -- very Mediterranean. I grew up with banana trees, bougainvillea, oleander, prickly pear cactus, magnolia.

Living in France was an amazing adventure. I remember dinners outside in the long light evenings -- and foods I had never before seen: langoustines, raclettes, buckwheat galettes. I remember the dolmens, erected four or five thousand years ago and weathered by rain and salt air. I remember side trips to Mont St.-Michel with its extraordinary tides, and to Rennes to visit my host family's family. I remember going to the beach. I was determined to swim in the English Channel, even if it were cold!

And I remember noticing that plants grew in Brittany which I had never before seen. I was especially struck by the lush bushes covered with giant flowers made up of many tiny blooms. I asked my host mother what they were called, and she told me hortensias. Some years later I visited the island of Nantucket for the first time with the family who would become my in-laws, and there I saw the same beautiful clusters of blossoms again, and learned their common English name, which is hydrangea.

Hydrangeas grow all over coastal New England. They grow in our backyard now, too -- though in our backyard their blooms are a simple ivory-white. In more acidic soils, like the seaside soil of Lannion (or, for that matter, the seaside soil of Nantucket and Cape Cod), the blooms are blue: ranging from periwinkle, to pale lavender, to a deep purple-blue. They're a kind of natural litmus paper. And every time I see them, I remember for an instant what it was like to be fifteen on my homestay in Lannion.