While taking a train from London to Paris during the winter I noticed trees filled with big round nests.
I was is Paris for the New Year celebration! Every neighborhood had street vendors selling giant bunches of mistletoe on New Year's Eve, I told my friend Jenni (who have been living in France for a year) how impressed I was with the huge, lush bunches. She told me how they grow all over the countryside, in big round balls, on trees :)
Mistletoe is in fact a parasite, unable to grow without feeding from a host plant. It manages this by producing a specialized root system that searches for and then taps into the host plants own vascular system. This enables the mistletoe to draw water and nutrients directly from the host, although it is able to create some of its own sugars using limited photosynthesis. The mistletoe also releases growth regulation hormones into the host causing localized swelling and helping to increase the yield of nutrient and water.
From the earliest times mistletoe has been one of the most magical, mysterious, and sacred plants of European folklore. It was considered to bestow life and fertility.