The seersucker effect comes about because the dominant tuck stitch makes the piece shorter and wider than a plain stocking stitch piece with the same number of stitches and rows. The stitches in the columns where all stitches are knitted are longer than the tuck patterned stitches so they pucker.
The middle two columns are punched out so that the corresponding needles will knit every row. To get a neat selvedge, position the edge where there are columns of knit stitches.
I like the texture so much I will make another modified Card 7 with punched out columns on the edges as well as the center of the card.