Four-legged knot stitch
This cross stitch is formed by two crossed straight stitches, the second of which is knotted over the centre of the first one. It is normally worked as an evenly-spaced powdered filling, either with all of the crosses at a vertical orientation, or placed randomly.
Bring your needle up and take it down a short distance below to form a straight stitch - this is the first part of your cross.
Bring your needle back up to the right of the previous stitch and lay your thread horizontally over the middle of the straight stitch.
Leaving a loop to the left, bring your thread to the top right. Slide your needle under where the two threads cross and over the working thread.
Pull your thread taut to form the knot and take it down to make the fourth leg of the cross.
Structure of stitch
Mrs Archibald Christie, Samplers and Stitches (1921) , p.52
Kate Haxell, The Stitch Bible (2012)
Jennifer Campbell, Ann-Marie Bakewell, Guide to Embroidery Stitches (2004)
Sarah Whittle, The Needlecraft Stitch Directory (2012)