it has been transformed, except in a few taxa where lobules are always explanate, into a galeate water-sac, which is formed wholly from the lobule, with the external surface from the adaxial leaf surface.
on the side that is towards the axis or central line, usually on the upper side
Heceleme
on the side that I·s to·wards the ax·is or cen·tral line, u·su·al·ly on the up·per side