There are two variations. The first is worked with two parallel lines of Stem Stitch with groups of three horizontal Satin Stitches placed at intervals in between. The Satin Stitch clusters are then laced together in both directions. A French Knot is placed in the middle of the loops. The second variation is much simplified with only the groups of three or more horizontal Satin Stitches threaded together.
Mary Thomas's Dictionary of Embroidery Stitches, p 110 The Stitches of Creative Embroidery, p 56