facet_form(horiz = NULL, horiz2 = NULL, vert = NULL, vert2 = NULL)horiz) and second (horiz2) level of faceting in
the horizontal direction. E.g. "M" or "species". A value of NULL (default)
indicates no faceting.vert) and second (vert2) level of faceting in
the vertical direction. E.g. "M" or "species". A value of NULL (default)
indicates no faceting.facet_grid, or NULL if all
arguments are NULL