Modern pagans are wont to promote a certain "Celtic Tree Calendar" which has thirteen months, named for trees, based upon the ogham alphabet. Some of them assert that the Celts followed this calendar, and that proof of this can be found in the existence of ogham, and in the works of Robert Graves. Unfortunately, this is as false as the assertion that the druids built Stonehenge.
First, it should be stated that like most (if not all) human civilizations, the Celts had a calendar--one which existed before the Romans, or at least independent of the Romans. It is known from Irish literature that there were four important holidays in the year--Samhain, Imbolc, Beltane, and Lughnassadh--and from archaeological findings (namely stone chambers, circles, etc.) it is possible they adopted the solstices and equinoxes, though these were not as important, but considered "mid" days (hense "midwinter," "midsummer").
And I admit, I copied all this down and made a pretty table in my BoS that had all the months with their corresponding trees listed beside them all while having no idea that this was based off a book a man had written 50-some years ago with no proof behind it.
I am part of a Celtic Paganism group on facebook and one of the members shared the article below which explains a little more on why it's false. While it doesn't attack Robert Graves like one would expect, it does clarify things.
As a side note, there WILL be a divine Friday tomorrow. It's been missing because of Hurricane Irene blowing through here but that's over and done with now. :)