The paper focuses on the instability of planar smectic layers like the undulation instability. This time it is not caused by the dilatation, but by the director tile away from the layer normal - effective dilatation. We are especially interested in the formation of onions. It appears that the key is a local perforation of layers, which can be desribed by a variable degree of smectic order.
We set up a theoretical description of the polymer nematic with director-density coupling, which enables a proper description of defects. We calculate various configurations of DNA packed into a hard sphere.