Read it through once

It is often very difficult to say why certain plants have received so much attention and veneration in ancient times. In some cases it is clearly because they are poisonous, and therefore become dreadful and awe-inspiring. Why, however, should a twig of Rowan (_Pyrus Aucuparia_) be so often placed above the door of a Highland cottage? In some way it was supposed to keep off evil spirits, but there is no special reason why it should have been chosen.