The Tree is also often found in Psalters, especially English manuscripts, illustrating the B initial of "Beatus Vir", the beginning of Psalm 1, which often occupies a whole page. Sometimes this is the only fully illuminated page, and if it is historiated (i.e. contains a pictured scene) the Tree is the usual subject. When not historiated, the initial had for about two hundred years been most often made up of, or filled with, spiraling plant tendrils, often with animals or men caught up in them, so the development to the tree was a relatively easy step. Indeed, although Jesse's son David was believed to be the author of the Psalms, it has been suggested that the tradition of using a Jesse Tree here arose largely because it was an imposing design that worked well filling a large B shape.