Polar bar

Plastid

 

Porca

A polar bar is a hyaline thickening of silica, present at the apices in some pennate species. The genus Sellaphora possesses variable development of polar bars.

Alternative Term

transapical thickening

Some authors use "transapical thickening", rather than polar bar.

Image Credit: Marina Potapova

Scanning electron micrograph of Sellaphora wallacei showing the polar bar at the apex.

Image Credit: Marina Potapova

Light micrograph of Sellaphora rexii, with the thickening of the polar bar appearing lighter than other parts of the valve.