If you took tree or plant physiology, you may remember lammas shoots. According to Kozlowski here it’s because in England they occur around Lammas Day, the first of August. Also according to Kozlowski, they are called “Johannastriebe” in German and St. Martin’s shoots in France, after those saints feastdays.
Here is a recent (2011?) poster studying lammas shoots in Norway spruce. Because a variety of genetic groups were planted at different locations, they can parse out the genetic and environmental components.